Editing Reverse Polish notation (section)

==== {{anchor|8-level RPN}}Community-developed hardware-based calculators ====
{{See also|#Hewlett-Packard{{!}}Hewlett-Packard RPN calculators}}
An eight-level stack was suggested by John A. Ball in 1978.<ref name="Ball_1978"/>

The community-developed calculators [[WP&nbsp;34S]] (2011<!-- with some initial planning going back to 2008 -->), [[WP&nbsp;31S]] (2014) and [[WP&nbsp;34C]] (2015), which are based on the [[HP&nbsp;20b]]/[[HP&nbsp;30b]] hardware platform, support classical Hewlett-Packard-style reverse Polish notation supporting automatic stack lift behaviour of the {{key press|Enter {{larger|↑}}}} key and top register copies on pops, but switchable between a four- and an eight-level operational stack.

In addition to the optional support for an eight-level stack, the newer [[SwissMicros DM42]]-based [[WP&nbsp;43S]] as well as the [[WP&nbsp;43C]] (2019)&nbsp;/ [[C43 (calculator)|C43]] (2022)&nbsp;/ [[C47 (calculator)|C47]] (2023) derivatives support data types for stack objects (real numbers, infinite integers, finite integers, complex numbers, strings, matrices, dates and times). The latter three variants can also be switched between ''classical'' and ''entry RPN'' behaviour of the {{key press|Enter {{larger|↑}}}} key, a feature often requested by the community.<ref name="Paul_2015"/> They also support a rarely seen [[significant figure]]s mode, which had already been available as a compile-time option for the WP&nbsp;34S and WP&nbsp;31S.<ref name="Bit_2014"/><ref name="Bit_2015"/>

Since 2021, the [[HP-42S]] simulator [[Free42]] version 3<!-- (aka [[Plus42]] version 1) --> can be enabled to support a dynamic RPN stack only limited by the amount of available memory instead of the classical 4-level stack. This feature was incorporated as a selectable function into the DM42 since firmware DMCP-3.21&nbsp;/ DM42-3.18.<ref>https://forum.swissmicros.com/viewtopic.php?f=16&t=2939<!-- UPDATE: DMCP-3.21 / DM42-3.18 2021-04-17 https://web.archive.org/web/20230923132306/https://forum.swissmicros.com/viewtopic.php?f=16&t=2939 --></ref><ref>https://forum.swissmicros.com/viewtopic.php?f=15&t=2845<!-- Free42 Version 3 2021-02-24 https://web.archive.org/web/20230923135327/https://forum.swissmicros.com/viewtopic.php?f=15&t=2845 --></ref>