The "k" is the constant you're trying to determine—it's related to your metabolic clearance rate for testosterone. When you multiply it by the dose rate you get an estimate for free testosterone:
free_testosterone = constant * dose_rate
The units for free testosterone and dose rate can be whatever's convenient. But you have to be consistent. For example, you could have free testosterone in ng/dL and dose in mg T/week. Note that the latter is different from mg of testosterone cypionate per week. You must multiply the milligrams of testosterone cypionate by 0.7 to get milligrams of testosterone.
In addition, you have to be consistent with the method used to obtain free testosterone. There are basically two choices, and ideally you'd track using both methods to see if results are similar. First, you can have a lab measure free testosterone via equilibrium dialysis. Second, you can have a lab measure total testosterone, SHBG and maybe albumin in order to calculate free testosterone with Vermeulen's equation.
If your'e willing to get lab work twice before changing to a lower injection frequency then I would wait 4-6 weeks after staring injections before getting the first set of tests. Based on these results you may want to adjust the dose to target appropriate serum levels, then repeat testing in another 4-6 weeks. At that time you would hopefully have a decent idea of your proportionate response to dose, and could then experiment with less burdensome protocols.
Ideally it's good to give any particular protocol three months before deciding about changes that are driven by subjective criteria.
