I use my spotmeter with a reverse mounted 50mm camera lens for 35mm and a small light table with a sheet of black construction paper w a hole cut out.
I did not build the stand but hand hold the meter.

Since all I am looking for is the difference between fb+fog and the zone I neg etc I use the formula EV X 0.3010 to get the relative density.

So if the fb+fog neg = EV 10 then rel dens = 3.01
the tested zone I neg = EV 9.6 then rel dens = aprox 2.89
Difference = 3.01 - 2.89 or 0.12.

Close enough for my humble work.

It works for me. I would buy a real one on Ebay but have never had much luck in winning anything on Ebay unless I decide to use those sneeky programs that snipe at the last few seconds...