Yes, measuring a trough like this is pretty typical. The main problem with this approach is that it dampens awareness of how high serum testosterone goes right after injections. A rough estimate for cypionate is that on weekly injections peak serum testosterone could be as high as 2.5 to 3 times higher than the trough value. So you might measure 500 ng/dL and think it's lowish, but at the beginning of the cycle your levels are unnaturally elevated, e.g. 1,250-1,500 ng/dL. With greater awareness guys might be inclined to inject more often, which helps to prevent side effects.