I agree with Sandy, a good densitometer can be had at E bay for $300. and is a great tool to have. As Sandy suggested I did my BTZS testing and printing is a snap. I read the low value, the high value and print according the SBR I have. When I started printing pt/pd I did all this by the zone system, so I got a good neg, but I had to test prints, with the densitometer and the BTZS my first print is always close in exposure and contrast. I had to eat some crow and admit the BTZS is far easier than the zone system, and the desitometer is a complemetary tool to read your negs.
If you are using only the zone system, then you dont need one. You can have your negs read at a photo lab and if you stick with the same developer/film combination then things should be laways the same.