Doremus
I think your calculations are realistic. I think to remember that the shutter error can be as much as 2/3 stop at fast speeds and small apertures, but as Ian said above, that combination is unlikely due to film speeds and normal lighting situations. Your numbers are more 'real' world, and as you say, normal shutter speed variations are also within 1/3 stop. Sometimes they compensate, but unfortunately, in some cases (such as in cold weather conditions), they can also add to the problem.
By the way, these shutter issues are the reason that I advise against in-camera exposure series for film testing. Using a transmission step tablet is the best way to get an accurate exposure series.
I think your calculations are realistic. I think to remember that the shutter error can be as much as 2/3 stop at fast speeds and small apertures, but as Ian said above, that combination is unlikely due to film speeds and normal lighting situations. Your numbers are more 'real' world, and as you say, normal shutter speed variations are also within 1/3 stop. Sometimes they compensate, but unfortunately, in some cases (such as in cold weather conditions), they can also add to the problem.
By the way, these shutter issues are the reason that I advise against in-camera exposure series for film testing. Using a transmission step tablet is the best way to get an accurate exposure series.