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<div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><p class="mw-empty-elt"> </p> <style data-mw-deduplicate="TemplateStyles:r1257001546">.mw-parser-output .infobox-subbox{padding:0;border:none;margin:-3px;width:auto;min-width:100%;font-size:100%;clear:none;float:none;background-color:transparent}.mw-parser-output .infobox-3cols-child{margin:auto}.mw-parser-output .infobox .navbar{font-size:100%}@media screen{html.skin-theme-clientpref-night .mw-parser-output .infobox-full-data:not(.notheme)>div:not(.notheme)[style]{background:#1f1f23!important;color:#f8f9fa}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .infobox-full-data:not(.notheme) div:not(.notheme){background:#1f1f23!important;color:#f8f9fa}}@media(min-width:640px){body.skin--responsive .mw-parser-output .infobox-table{display:table!important}body.skin--responsive .mw-parser-output .infobox-table>caption{display:table-caption!important}body.skin--responsive .mw-parser-output .infobox-table>tbody{display:table-row-group}body.skin--responsive .mw-parser-output .infobox-table tr{display:table-row!important}body.skin--responsive .mw-parser-output .infobox-table th,body.skin--responsive .mw-parser-output .infobox-table td{padding-left:inherit;padding-right:inherit}}</style><table class="infobox"><caption class="infobox-title">HP-55</caption><tbody><tr><td colspan="2" class="infobox-image"><span class="mw-default-size" typeof="mw:File/Frameless"><a href="/wiki/File:HP_55_Calculator.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e3/HP_55_Calculator.jpg/220px-HP_55_Calculator.jpg" decoding="async" width="220" height="372" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/e3/HP_55_Calculator.jpg/330px-HP_55_Calculator.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/e3/HP_55_Calculator.jpg/440px-HP_55_Calculator.jpg 2x" data-file-width="1400" data-file-height="2370" /></a></span><div class="infobox-caption">HP-55.</div></td></tr><tr><th scope="row" class="infobox-label">Type</th><td class="infobox-data"><a href="/wiki/Programmable_calculator" title="Programmable calculator">Programmable</a></td></tr><tr><th scope="row" class="infobox-label">Introduced</th><td class="infobox-data">1975</td></tr><tr><th colspan="2" class="infobox-header">Calculator</th></tr><tr><th scope="row" class="infobox-label">Entry mode</th><td class="infobox-data"><a href="/wiki/RPN_input_mode" class="mw-redirect" title="RPN input mode">RPN</a></td></tr><tr><th scope="row" class="infobox-label">Display type</th><td class="infobox-data">Red <a href="/wiki/Light-emitting_diode" title="Light-emitting diode">LED</a> <a href="/wiki/Seven-segment_display" title="Seven-segment display">seven-segment display</a></td></tr><tr><th scope="row" class="infobox-label">Display size</th><td class="infobox-data">15 digits (decimal point uses one digit), (±10<sup>±99</sup>)</td></tr><tr><th colspan="2" class="infobox-header">Programming</th></tr><tr><th scope="row" class="infobox-label">Programming language(s)</th><td class="infobox-data"><a href="/wiki/Reverse_Polish_Notation" class="mw-redirect" title="Reverse Polish Notation">RPN</a> key stroke</td></tr><tr><th colspan="2" class="infobox-header">Other</th></tr><tr><th scope="row" class="infobox-label">Power supply</th><td class="infobox-data">Internal rechargeable battery or 115/230 V AC, 5 W</td></tr><tr><th scope="row" class="infobox-label">Weight</th><td class="infobox-data">Calculator: 9 oz (260 g),<br />recharger: 5 oz (140 g)</td></tr><tr><th scope="row" class="infobox-label">Dimensions</th><td class="infobox-data">Length: 5.8 inches (150 mm),<br />width: 3.2 inches (81 mm),<br />height: 0.7–1.3 inches (18–33 mm)</td></tr></tbody></table> <p>The <b>HP-55</b> was a programmable handheld calculator, a lower-cost alternative to the <a href="/wiki/HP-65" title="HP-65">HP-65</a>. Introduced by <a href="/wiki/Hewlett-Packard" title="Hewlett-Packard">Hewlett-Packard</a> in 1975, it featured twenty storage registers and room for 49 keystroke instructions. Its outward appearance was similar to the HP-65, but its silver band went through between the display and the keyboard like <a href="/wiki/HP-45" title="HP-45">HP-45</a>, and the functions of some keys were different from HP-65, and it did not have a magnetic card reader/writer. Like all Hewlett-Packard calculators of the era and most since, the HP-55 used <a href="/wiki/Reverse_Polish_Notation" class="mw-redirect" title="Reverse Polish Notation">Reverse Polish Notation</a> (RPN) and a four-level automatic operand <a href="/wiki/Stack_(data_structure)" class="mw-redirect" title="Stack (data structure)">stack</a>. </p><p>Another feature of the <b>HP-55</b> was that it officially featured a stop-watch function much similar to the hidden stop-watch function of the earlier <b><a href="/wiki/HP-45" title="HP-45">HP-45</a></b> calculator. This stop-watch function could be accessed by setting the mode-slider to the Timer position. A quartz-crystal inside the calculator provided an accurate timebase, and it was advertised that the timer ran with as little as +/- 0.01% error. The data format used by the stop-watch consisted of a combination of units (Hours, Minutes and Seconds), but the <b>HP-55</b> featured a special conversion function to convert between this format and a pure unit (Hours). Because of this, data from the stop-watch could easily be used right away in calculations. </p><p>The <b>HP-55</b> also featured several other conversion functions to instantly convert data between the <a href="/wiki/United_States_customary_units" title="United States customary units">Imperial</a> and <a href="/wiki/Metric_system" title="Metric system">Metric</a> systems. </p><p><a href="/wiki/Bill_Hewlett" title="Bill Hewlett">Bill Hewlett</a>'s design requirement was that the calculator should fit in his shirt pocket. That is one reason for the tapered depth of the calculator. The documentation for the programs in the calculator is complete, including algorithms for hundreds of applications, including the solutions of differential equations, stock price estimation, statistics, and so forth. </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=HP-55&action=edit&section=1" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/HP-45" title="HP-45">HP-45</a></li> <li><a href="/wiki/HP-65" title="HP-65">HP-65</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=HP-55&action=edit&section=2" title="Edit section: External links"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a rel="nofollow" class="external text" href="http://mycalcdb.free.fr/main.php?l=0&id=777">The HP-55</a> at an unofficial Hewlett-Packard museum (<a rel="nofollow" class="external text" href="http://mycalcdb.free.fr">MyCalcDB</a>).</li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20100707155439/http://archive.computerhistory.org/resources/text/HP/HP.PocketCalc.1975.102646259.pdf">1975 HP Calculator Christmas Guide</a></li> <li><a rel="nofollow" class="external text" href="http://www.hpmuseum.org/hp55.htm">HP-55</a> page at the unofficial Museum of HP Calculators</li></ul> <div class="navbox-styles"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output 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href="/wiki/Template:HP_calculators" title="Template:HP calculators"><abbr title="View this template" style="color:#FFFFFF">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:HP_calculators" title="Template talk:HP calculators"><abbr title="Discuss this template" style="color:#FFFFFF">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:HP_calculators" title="Special:EditPage/Template:HP calculators"><abbr title="Edit this template" style="color:#FFFFFF">e</abbr></a></li></ul></div><div id="Hewlett-Packard_(HP)_calculators" style="font-size:114%;margin:0 4em"><a href="/wiki/HP_calculators" title="HP calculators"><span style="color:#FFFFFF;">Hewlett-Packard (HP) calculators</span></a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%;background-color: #FFFFFF"><a href="/wiki/Comparison_of_HP_graphing_calculators" title="Comparison of HP graphing calculators">Graphing</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/HP_9g" title="HP 9g">9g</a></li> <li><a href="/wiki/HP-28_series#HP_28C" title="HP-28 series">28C</a></li> <li><a href="/wiki/HP-28_series#HP_28S" title="HP-28 series">28S</a></li> <li><a href="/wiki/HP_38G" title="HP 38G">38G</a></li> <li><a href="/wiki/HP_39/40_series#39G" title="HP 39/40 series">39G</a></li> <li><a href="/wiki/HP_39/40_series#39g+" title="HP 39/40 series">39g+</a></li> <li><a href="/wiki/HP_39/40_series#39gs" title="HP 39/40 series">39gs</a></li> <li><a href="/wiki/HP_39/40_series#39gII" title="HP 39/40 series">39gII</a></li> <li><a href="/wiki/HP_39/40_series#40G" title="HP 39/40 series">40G</a></li> <li><a href="/wiki/HP_39/40_series#40gs" title="HP 39/40 series">40gs</a></li> <li><a href="/wiki/HP_48_series#48S" title="HP 48 series">48S</a></li> <li><a href="/wiki/HP_48_series#48SX" title="HP 48 series">48SX</a></li> <li><a href="/wiki/HP_48_series#48G" title="HP 48 series">48G</a></li> <li><a href="/wiki/HP_48_series#48G+" title="HP 48 series">48G+</a></li> <li><a href="/wiki/HP_48_series#48GX" title="HP 48 series">48GX</a></li> <li><a href="/wiki/HP_49/50_series#48gII" title="HP 49/50 series">48gII</a></li> <li><a href="/wiki/HP_49/50_series#49G" title="HP 49/50 series">49G</a></li> <li><a href="/wiki/HP_49/50_series#49g+" title="HP 49/50 series">49g+</a></li> <li><a href="/wiki/HP_49/50_series#50g" title="HP 49/50 series">50g</a></li> <li><a href="/wiki/HP_Prime" title="HP Prime">Prime</a></li> <li><a href="/wiki/HP_Xpander" title="HP Xpander">Xpander</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;background-color: #FFFFFF">Scientific programmable</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Hewlett-Packard_Voyager_series#10C" title="Hewlett-Packard Voyager series">10C</a></li> <li><a href="/wiki/Hewlett-Packard_Voyager_series#11C" title="Hewlett-Packard Voyager series">11C</a></li> <li><a href="/wiki/HP-15C" title="HP-15C">15C</a> <ul><li><a href="/wiki/HP-15C#15CLE" title="HP-15C">LE</a></li> <li><a href="/wiki/HP-15C#15CCE" title="HP-15C">CE</a></li></ul></li> <li><a href="/wiki/HP-16C" title="HP-16C">16C</a></li> <li><a href="/wiki/HP-19C/-29C#19C" title="HP-19C/-29C">19C</a></li> <li><a href="/wiki/HP-20S" title="HP-20S">20S</a></li> <li><a href="/wiki/HP-21S" class="mw-redirect" title="HP-21S">21S</a></li> <li><a href="/wiki/HP-25#25" title="HP-25">25</a></li> <li><a href="/wiki/HP-25#25C" title="HP-25">25C</a></li> <li><a href="/wiki/HP-19C/-29C#29C" title="HP-19C/-29C">29C</a></li> <li><a href="/wiki/HP-32S" title="HP-32S">32S</a></li> <li><a href="/wiki/HP-32SII" class="mw-redirect" title="HP-32SII">32SII</a></li> <li><a href="/wiki/HP-33E/C" class="mw-redirect" title="HP-33E/C">33C</a></li> <li><a href="/wiki/HP-33E/C" class="mw-redirect" title="HP-33E/C">33E</a></li> <li><a href="/wiki/HP_33s" title="HP 33s">33s</a></li> <li><a href="/wiki/HP-34C" title="HP-34C">34C</a></li> <li><a href="/wiki/HP_35s" title="HP 35s">35s</a></li> <li><a href="/wiki/HP-41C" title="HP-41C">41C</a></li> <li><a href="/wiki/HP-41C#The_HP-41CV_and_CX" title="HP-41C">41CV</a></li> <li><a href="/wiki/HP-41C#The_HP-41CV_and_CX" title="HP-41C">41CX</a></li> <li><a href="/wiki/HP-42S" title="HP-42S">42S</a></li> <li><a class="mw-selflink selflink">55</a></li> <li><a href="/wiki/HP-65" title="HP-65">65</a></li> <li><a href="/wiki/HP-67/97#67" title="HP-67/97">67</a></li> <li><a href="/wiki/HP-71B" title="HP-71B">71B</a></li> <li><a href="/w/index.php?title=HP-95C&action=edit&redlink=1" class="new" title="HP-95C (page does not exist)">95C</a></li> <li><a href="/wiki/HP-67/97#97" title="HP-67/97">97</a></li> <li><a href="/wiki/HP-67/97#97S" title="HP-67/97">97S</a></li> <li><a href="/wiki/Hewlett-Packard_9100A#9100A" title="Hewlett-Packard 9100A">9100A</a></li> <li><a href="/wiki/Hewlett-Packard_9100A#9100B" title="Hewlett-Packard 9100A">9100B</a></li> <li><a href="/w/index.php?title=Hewlett-Packard_9805&action=edit&redlink=1" class="new" title="Hewlett-Packard 9805 (page does not exist)">9805</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;background-color: #FFFFFF">Scientific non-programmable</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/w/index.php?title=HP_6s&action=edit&redlink=1" class="new" title="HP 6s (page does not exist)">6s</a></li> <li><a href="/w/index.php?title=HP_6s&action=edit&redlink=1" class="new" title="HP 6s (page does not exist)">6s Solar</a></li> <li><a href="/w/index.php?title=HP_8s&action=edit&redlink=1" class="new" title="HP 8s (page does not exist)">8s</a></li> <li><a href="/w/index.php?title=HP_9s&action=edit&redlink=1" class="new" title="HP 9s (page does not exist)">9s</a></li> <li><a href="/wiki/HP_10s" title="HP 10s">10s</a></li> <li><a href="/wiki/HP_10s#10s+" title="HP 10s">10s+</a></li> <li><a href="/wiki/HP_10s#10sII" title="HP 10s">10sII</a></li> <li><a href="/wiki/HP-21" title="HP-21">21</a></li> <li><a href="/wiki/HP-22S" title="HP-22S">22S</a></li> <li><a href="/wiki/HP-27" title="HP-27">27</a></li> <li><a href="/wiki/HP-27S" title="HP-27S">27S</a></li> <li><a href="/wiki/HP_30s" class="mw-redirect" title="HP 30s">30s</a></li> <li><a href="/wiki/HP-31E" class="mw-redirect" title="HP-31E">31E</a></li> <li><a href="/wiki/HP-32E" class="mw-redirect" title="HP-32E">32E</a></li> <li><a href="/wiki/HP-35" title="HP-35">35</a></li> <li><a href="/wiki/HP-45" title="HP-45">45</a></li> <li><a href="/w/index.php?title=HP-46&action=edit&redlink=1" class="new" title="HP-46 (page does not exist)">46</a></li> <li><a href="/w/index.php?title=HP-91&action=edit&redlink=1" class="new" title="HP-91 (page does not exist)">91</a></li> <li><a href="/w/index.php?title=HP_SmartCalc_series&action=edit&redlink=1" class="new" title="HP SmartCalc series (page does not exist)">300s</a></li> <li><a href="/w/index.php?title=HP_SmartCalc_series&action=edit&redlink=1" class="new" title="HP SmartCalc series (page does not exist)">300s+</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;background-color: #FFFFFF">Financial and business</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/HP-10B#10B" title="HP-10B">10B</a></li> <li><a href="/wiki/HP-10B#10bII" title="HP-10B">10bII</a></li> <li><a href="/wiki/HP-10B#10bII+" title="HP-10B">10bII+</a></li> <li><a href="/wiki/HP-12C#12C" title="HP-12C">12C</a> <ul><li><a href="/wiki/HP-12C#12c_Platinum" title="HP-12C">Platinum</a></li> <li><a href="/wiki/HP-12C#12c_Prestige" title="HP-12C">Prestige</a></li></ul></li> <li><a href="/w/index.php?title=HP-14B&action=edit&redlink=1" class="new" title="HP-14B (page does not exist)">14B</a></li> <li><a href="/wiki/HP-17B" title="HP-17B">17B</a></li> <li><a href="/wiki/HP-17B#17BII" title="HP-17B">17BII</a></li> <li><a href="/wiki/HP-17B#17bII+" title="HP-17B">17bII+</a></li> <li><a href="/wiki/HP-18C" title="HP-18C">18C</a></li> <li><a href="/wiki/HP-19B" title="HP-19B">19B</a></li> <li><a href="/wiki/HP-19B#19BII" title="HP-19B">19BII</a></li> <li><a href="/wiki/HP_20b" title="HP 20b">20b</a></li> <li><a href="/wiki/HP-22" title="HP-22">22</a></li> <li><a href="/wiki/HP-27" title="HP-27">27</a></li> <li><a href="/wiki/HP_30b" title="HP 30b">30b</a></li> <li><a href="/wiki/HP-37E" class="mw-redirect" title="HP-37E">37E</a></li> <li><a href="/wiki/HP-38E/C#38C" class="mw-redirect" title="HP-38E/C">38C</a></li> <li><a href="/wiki/HP-38E/C#38E" class="mw-redirect" title="HP-38E/C">38E</a></li> <li><a href="/w/index.php?title=HP-70&action=edit&redlink=1" class="new" title="HP-70 (page does not exist)">70</a></li> <li><a href="/w/index.php?title=HP-80&action=edit&redlink=1" class="new" title="HP-80 (page does not exist)">80</a></li> <li><a href="/w/index.php?title=HP-81&action=edit&redlink=1" class="new" title="HP-81 (page does not exist)">81</a></li> <li><a href="/w/index.php?title=HP-92&action=edit&redlink=1" class="new" title="HP-92 (page does not exist)">92</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;background-color: #FFFFFF">Other</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/HP-01" title="HP-01">01</a></li> <li><a href="/w/index.php?title=Hewlett-Packard_HP-10&action=edit&redlink=1" class="new" title="Hewlett-Packard HP-10 (page does not exist)">10</a></li> <li><a href="/wiki/HP_CalcPad_series" title="HP CalcPad series">CalcPad</a> <ul><li><a href="/wiki/HP_CalcPad_series#100" title="HP CalcPad series">100</a></li> <li><a href="/wiki/HP_CalcPad_series#200" title="HP CalcPad series">200</a></li></ul></li> <li><a href="/w/index.php?title=HP_QuickCalc_series&action=edit&redlink=1" class="new" title="HP QuickCalc series (page does not exist)">QuickCalc</a></li> <li><a href="/w/index.php?title=HP_EasyCalc_series&action=edit&redlink=1" class="new" title="HP EasyCalc series (page does not exist)">EasyCalc</a></li> <li><a href="/w/index.php?title=HP_OfficeCalc_series&action=edit&redlink=1" class="new" title="HP OfficeCalc series (page does not exist)">OfficeCalc</a></li> <li><a href="/w/index.php?title=HP_PrintCalc_series&action=edit&redlink=1" class="new" title="HP PrintCalc series (page does not exist)">PrintCalc</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;background-color: #FFFFFF">Related topics</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Reverse_Polish_notation" title="Reverse Polish notation">RPN</a></li> <li><a href="/wiki/RPL_(programming_language)" title="RPL (programming language)">RPL</a></li> <li><a href="/wiki/Prime_Programming_Language" class="mw-redirect" title="Prime Programming Language">PPL</a></li> <li><a href="/wiki/FOCAL_(Hewlett-Packard)" class="mw-redirect" title="FOCAL (Hewlett-Packard)">FOCAL</a></li> <li><a href="/wiki/Algebraic_input_method" class="mw-redirect" title="Algebraic input method">ALG</a></li> <li><a href="/wiki/Computer_algebra_system" title="Computer algebra system">CAS</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;background-color: #FFFFFF">Emulation software</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/WRPN_Calculator" title="WRPN Calculator">16C</a></li></ul> </div></td></tr></tbody></table></div>    </div><noscript><img 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