When I was starting out I just did as many reps as comfortable in the prescribed time period and then matched the level by the fewest reps completed in any exercise. e.g. I started at A+ for chart 1 for 2 consecutive days, then A+ chart 2 for 3 days, then progressed upwards from chart3 D- as I only did 20 reps of ex. 1.

I failed chart 5, 2 days in a row 30 days ago and have only been doing chart 4 since then, but I exceed the A+ requirements (this morning: 32,24,50,45,450). Tomorrow will try chart 5 again.