Claire's process is a good way to get you pretty close claibrations and fairly easy. I was fortunate enough to get a densitometer a couple of years ago and now use it to get reasonably accurate calibrations of my exposures. I have also used my darkroom color analyzer to get good relative readings -- which is really the same as described in Claire's message. To add to this... since you have an enlarger, you can pick up a pretty good color analyzer for a few dollars these day (I saw one auction sell three at $5 for the lot) Shoot a roll and get some good numbers to work with.
Originally Posted by Claire Senft
Now, to relate this to the macro subject --
I learned that my variable power flashes are very inaccurate at the lower power settings:
I calibrated my variable power flashes for my macro set up... since I was getting pretty close to the subject, I really needed to crank the power down on my flashes. Let me tell you, I was amazed at how inacurate the dials and settings were in the low power settings. They're consistant, but way off from the control markings. Now that I know what to adjust to, my macro exposure is very predictable.
Summary: for macro work where you need to reduce the flash's power, expect the controls to be very inaccurate... testing really is worth the time.