For my black and white prints I just make a test strip where I am changing the times by a quarter stop per strip. For example 10, 12, 14, 17, and 20 seconds. This gives me a better spacing between exposures than a 5, 10, 15, 20 second strip.

For color I have a spread sheet printed out using the formula T2 = T1 (H2/H1)^1.94 where H1 is the original height from the center of the lens to the baseboard, H2 is the new height measured the same way, T1 is the exposure for H1, and T2 is the new exposure. I am using Omega enlargers and found that an exponent of 1.94 works better than the exponent of 2 required by the inverse square law. I adjust the aperture so that my exposures stay in the 10 to 20 second range.

Prior to this, again for color, I calibrated an EM10 exposure monitor so that it read directly in seconds and filed out the edge of my negative carrier so that I could always take a reading off the blank film between frames. Both systems have worked well for me.