I don’t know if an app is available but I would print out the proctor curve and plot those points manually or in EXCEL. Why do you need the app? For using it at the field?
I sometime train earthwork inspectors. Everything will be done by phone in future. So I was looking for something for them to check if they get percent compaction results. So the lab could send the inspector not just the percent compaction but also the dry density and moisture content so they could see if the test result is reasonable.
Apps are nice, but for this, I would just use a hard copy of the proctor curves and check where the information provided by the lab fits in that plot...
I give the contractor's staff doing the tests a laminated graph showing the ZAV. Whether you use 2.64 or 2.66 - doesn't make much difference - but bloody make sure the field tests results lie to the left of the line.