If you are going to use f-stop timing for test strips, the chart found at Ralph Lambrecht's site (darkroommagic.com) works well, with one caution.
The chart is really set up to aid in doing fine adjustments, burns and dodges, where you are adding to or subtracting from an already determined base exposure. When you are making a test strip, you don't necessarily have a base starting point, and you are wanting to cover a range of possibilities. In addition, test strips work best if you don't start and stop - i.e. it is better to start with the whole strip uncovered, and then progressively cover more of the strip, at the required intervals.
This involves a bit of a challenge, because the fractional f-stops listed on the darkroommagic site are hard to accurately count with either a metronome or sweep second hand or in your head (I've never been able to get those 1/10 second intervals to come out right myself).
Also, when you are starting out with the entire strip uncovered, and then progressively covering more over, the segment times add up - if you were using the same interval (e.g. 4 seconds) the progression would be as follows:
1st = 4 seconds
2nd = 4 + 4 = 8 seconds
3rd = 4 + 4 + 4 = 12 seconds
4th = 4 + 4 + 4 + 4 = 16 seconds
etc., etc.
What I like to do is to do my test strips in 1/2 stop intervals, and to use the (almost) standard f-stop progression on my lenses as a guide - i.e. 5.6, 8, 11, 16, 22, 32, 45, 64. To accomplish this, I set my timer to 64 seconds, turn on the "metronome" function, begin with the strip entirely uncovered, and then progressively cover over segments of the strip as follows:
1st = 6 seconds (entire strip uncovered)
2nd = 6 + 2 = 8 seconds (all but 1st segment uncovered)
3rd = 6 + 2 + 3 = 11 seconds (all but 1st & 2nd segment uncovered)
4th = 6 + 2 + 3 + 5 = 16 seconds etc.
5th = 6 + 2 + 3 + 5 + 6 = 22 seconds etc.
6th = 6 + 2 + 3 + 5 + 6 + 10 = 32 seconds etc.
7th = 6 + 2 + 3 + 5 + 6 + 10 + 13 = 45 seconds (last 2 segments uncovered)
8th = 6 + 2 + 3 + 5 + 6 + 10 + 13 + 19 = 64 seconds (last segment only)
To ease the process, I have a chart with the sequence of intervals by my easel: 6, 2, 3, 5, 6, 10, 13, 19 - in big, easily read numerals.
I use 6 seconds rather than 5.6 seconds to start because, well, I can't count 5.6 seconds with the necessary precision, but with the aid of the "metronome" on my timer, I can get pretty close to 6.
Once you find a segment that is close, you can then generally do a further test with finer divisions within that segment, using the chart (but again calculating the differences between sub-segments).
Hope this helps.
Matt
P.S. If any one else finds the 6, 2, 3, 5, 6, 10, 13, 19 chart useful, please feel free to make whatever use of it you wish - no copyright concerns here
