This link will bring you to a PDF copy of the 203 instruction manual booklet,
print it out and put it to your camera its valuable.
The RF Calculator is intersting and it works if your lightmeter is lost or still at home.
Here you can read how it works:

http://www.cameramanuals.org/pdf_files/seagull_203.pdf

Yeah never adjust exposure and aperture after cocking a compur.