According to online help the function of "set page variable" and "show page variable" is: Set page variable Inserts a reference point in the document, after which the page count restarts. Select "on" to enable the reference point, and "off" to disable it. You can also enter an offset to start the page count at a different number. Show page variable Displays the number of pages from the "Set page variable" reference point to this field. The real function is: Set page variable: Changes page number from the current page. Show page variable: this field seems to be always blank. I am reporting this from my cellphone, after getting feedback from ask.libreoffice.org. When I get to my home I will update with details of libreoffice version. It seems a persistent old bug because methods to count oages in a chapter I find in ask.libreoficce dont mention "show page variable", but they do mention "set page variable" to change current page number.
I confirm behaviour is buggy. Field _Show page variable_ inserts nothing (empty result), no matter what the value of the preceding _Set page variable_ is. Tested with 7.6.7.2 and 24.2.6.2
It is not a problem of documentation, but the feature is broken. It worked somehow (see below) in Version: 6.5.0.0.alpha0+ (x64) Build ID: 147af9e2cf7f937ed83ab00574b6a418a2cb629e CPU threads: 32; OS: Windows 10.0 Build 22631; UI render: default; VCL: win; Locale: de-DE (de_DE); UI-Language: en-US Calc: threaded and is broken in Version: 7.6.7.2 (X86_64) / LibreOffice Community Build ID: dd47e4b30cb7dab30588d6c79c651f218165e3c5 CPU threads: 32; OS: Windows 10.0 Build 22631; UI render: Skia/Vulkan; VCL: win Locale: de-DE (de_DE); UI: en-US Calc: threaded The feature worked from point of user in version 6.5. But the file format was already faulty at that time: The attribute text:active (19.755, ODF 1.3) of the <text:page-variable-set> element was/is not written to file. Its default value is 'false', so in case the page variable is 'on', the attribute has to be written to file. This error is inherited from OOo.