BTW, when not using a step tablet, you have to calculate the exposure individually for each step so that each one takes the same amount of "logarithmic" exposure, see below:

1. Target total test exposure time: 10minutes,
2. Each step: 1/3 stop, (pick your own values for these)

then

10:00 (start timer, none of the steps are covered)
07:56 (cover the first step)
06:18 (cover the second step)
05:00 (so on...)
03:58
03:08
02:30
01:58
01:34
01:15
01:00 (cover the 10th step, there should be one more step remaining, that will be exposed for the last minute...)

To find the correct slices for a different total exposure and/or step resolution you can use the formulas below:

1. To increase: time * (2 ^ (step)),
2. To decrease: time / (2 ^ (step))

Example:
1. 10:00 + 1/3 stop = 10 * (2 ^ (1 / 3)) = 12,60 = 12:36,
2. 10:00 - 1/3 stop = 10 / (2 ^ (1 / 3)) = 7,94 = 07:56

Since that's a real PITA (both calculating and waiting before the exposure unit for an impractical and dangerous duration - UVA is not good for skin and eyes!!!), most people prefer using step tablets.

Regards,
Loris.