As the NanoVNA project is open source the code is ever evolving and the units that ship from China now come with older firmware installed. If you want to test the very latest experimental code, you need to compile it on a PC, and then flash the firmware into the NanoVNA. Ohan's guide covers this all. For example, one recent update now enables time-domain reflectometry for measuring coax cable length, which we explored in a previous post.
Alternatively according to the GitHub readme, it is also possible to use a docker image which will remove the need to install the arm tool chain. Ready to flash images are also released every few days over on the GitHub release page, although these won't include the very latest or experimental changes.
Earlier in the month we posted about the NanoVNA, an open source VNA project by @edy555 and ttrftech that has recently become extremely affordable at US$50 for a fully assembled unit thanks to Chinese manufacturing.
Nucclearrambo provides a Python script which can be used with the NanoVNA's S1P output data to create a TDR graph. His tests with RG405 and LMR200 cable show that the length reported by the script comes remarkably close to the actual length.