Amount of voltage drop is load dependent.
This device only will tell you what the results are for a few select amounts of current
But it is just another tool you can use to help identify possible problems. It is not the judge & jury but I think it is still a nifty tool.
Here are some hand calcs for various "test" loads and pre-existing loads (I don't know what the actual test load characteristics are in the Ideal meter).
Examples for a 100 ft run of #12:
10A & 20A test for pre-existing 5A load at various pf:
#1) 60%pf 5 amp = 0.92% (pre-existing load)
#2) 10A 100% pf = 2.93% (test with no pre-existing load)
#3) combined = 4.25% (test with pre-existing load)
#4) #3 less #1 = 3.33% (0.40% difference)
#1) 60%pf 5 amp = 0.92% (pre-existing load)
#2) 20A 100% pf = 5.87% (test with no pre-existing load)
#3) combined = 7.26% (test with pre-existing load)
#4) #3 less #1 = 6.35% (0.48% difference)
#1) 80%pf 5 amp = 1.20% (pre-existing load)
#2) 10A 100% pf = 2.93% (test with no pre-existing load)
#3) combined = 4.33% (test with pre-existing load)
#4) #3 less #1 = 3.13% (0.20% difference)
#1) 80%pf 5 amp = 1.20% (pre-existing load)
#2) 20A 100% pf = 5.87% (test with no pre-existing load)
#3) combined = 7.30% (test with pre-existing load)
#4) #3 less #1 = 6.10% (0.24% difference)
#1) 92%pf 5 amp = 1.37% (pre-existing load)
#2) 10A 100% pf = 2.93% (test with no pre-existing load)
#3) combined = 4.38% (test with pre-existing load)
#4) #3 less #1 = 3.01% (0.08% difference)
#1) 92%pf 5 amp = 1.37% (pre-existing load)
#2) 20A 100% pf = 5.87% (test with no pre-existing load)
#3) combined = 7.33% (test with pre-existing load)
#4) #3 less #1 = 5.96% (0.09% difference)
10A & 20A test for pre-existing 10A load at various pf:
#1) 60%pf 10 amp = 1.85% (pre-existing load)
#2) 10A 100% pf = 2.93% (test with no pre-existing load)
#3) combined = 5.34% (test with pre-existing load)
#4) #3 less #1 = 3.50% (0.56% difference)
#1) 60%pf 10 amp = 1.85% (pre-existing load)
#2) 20A 100% pf = 5.87% (test with no pre-existing load)
#3) combined = 8.50% (test with pre-existing load)
#4) #3 less #1 = 6.66% (0.79% difference)
#1) 80%pf 10 amp = 2.41% (pre-existing load)
#2) 10A 100% pf = 2.93% (test with no pre-existing load)
#3) combined = 5.63% (test with pre-existing load)
#4) #3 less #1 = 3.22% (0.29% difference)
#1) 80%pf 10 amp = 2.41% (pre-existing load)
#2) 20A 100% pf = 5.87% (test with no pre-existing load)
#3) combined = 8.67% (test with pre-existing load)
#4) #3 less #1 = 6.26% (0.39% difference)
#1) 92%pf 10 amp = 2.74% (pre-existing load)
#2) 10A 100% pf = 2.93% (test with no pre-existing load)
#3) combined = 5.79% (test with pre-existing load)
#4) #3 less #1 = 3.05% (0.12% difference)
#1) 92%pf 10 amp = 2.74% (pre-existing load)
#2) 20A 100% pf = 5.87% (test with no pre-existing load)
#3) combined = 8.76% (test with pre-existing load)
#4) #3 less #1 = 6.02% (0.16% difference)