real aircraft instrument conversion to flight sim

Hello all,
I've recently joined this wealth of knowledge of a forum to try and carry out one of my most desired project within a flight simulator. I wish to convert an old altimeter I sourced (mk22 Canberra ) from being used on a real AC to being used on p3d, I've gutted out all the bits that aren't necessary for the project and I have been left with a stepper motor with its four wires, the dials and all the gearing. Last weekend I managed to get the thing to run using an L293d motor shield, an Arduino and some test code that made the stepper motor move. Now my problem is that I have no idea how to link the Arduino via link2fs, I know I have to obviously select the desired setting from link2fs and send it to P3D. But my issue more precisely is that I am completely lost with the coding that I need to write on the Arduino software. Has anyone here got any information, that could facilitate my headache? From what a kind youtuber and fellow forum colleague has emailed me is that I need to find out and tell the Arduino or link2fs where the start of my dial is, the end and its position etc... this to me is a bit of mystery as to how it works etc.

If anyone could help me and possibly give some ideas of the coding required or instructions on how to do so it would greatly appreciated.
I apologies in advance if anyone has already replied to such a feat!

many thanks to you all.
Marcelo