Sorry, but I know little about the Harrell powder measure but let me add this.
Powder accuracy of measurement is over rated as to how it effects the cartridge accuracy. Most good powder dispensers will give plus or minus 0.2 grains and that barely effect the resultant velocity. Yes, it effects the velocity but the other varibles swamp it out. My Dillion measure does that and the Redding Competition Model BR-30 claims even better. The latter has a much smaller measuring cup optimised for 30 grain loads and other loads around 30 grains. What is most important is the technique of using the measure. The claim is that it has to be operated the same way each time or the results will not be the same everytime.
While it is nice to strive to make every load perfect and exactly the same as the last, you may be beating a dead horse when you try to do better than throwing loads from an excellent powder measure like the Redding or even the Dillion for that matter. If you are benchrest shooting in competition it might make a difference (?) but they are shooting group sizes that range from 0.010 to 0.020 inches just to be competitive. Other factors are far more important in their shooting than perfectly weighed charges; like bullet selection, reloading technique. and shooting technique, not to even mention the expensive custom bench rest guns they use.