digital protractor for faceting machine

I am a new member here and am trying to find information of how to
build a digital protractor for a faceting machine. Had information
form a site that used a carbon trim pot, but the site has gone black.
from a search of this site I also see information on rotary encoders.

I need to know where I can get information of circuit s and such. also
any tutorials on electronics.

Thanks

O M