I use the Darkroom Automation Enlarging Meter for this purpose. It works very well as a baseboard densitometer, reading in stops with repeatability of about 0.02 stops in my experience. That's 0.006 optical density units. Overkill for a film curve, and less expensive than a decent used densitometer. I use a spreadsheet and type in the stops and let the spreadsheet convert to optical density (simply multiply by 0.3), calculate and subtract fb+f from a 'clear' area of the film, and draw the film curve.
Curious about the set up to use the enlarging meter, would save me the purchase of a densitometer. Thanks.