I think you're on track. Since you have a home brew densitometer, I be a little careful and check the readings it gives you. I've read the nice section on building one in Phil Davis's "Beyond the Zone Sytem" book. Sounds good but has some pitfalls that he talks about. The acid test is to measure a transmission reference with your densitometer and see if it agrees with what another one said. I have a 31 step transmission wedge from Stouffer (http://www.stouffer.net) that I sometimes use to check my densitometer. Pay the extra for them to put the acutal measurements of each step on the sleeve. It's still under $30 for the calibrated step wedge, I think.