You're gonna find that your Gem Pro 250 is NOT well suited to trickling up to a particular charge weight. As you trickle, at first nothing happens as the scale seems to want to "lock on" to the existing weight. Eventually, the silly scale takes the hint and changes the indication to a heavier weight, which may or may not be correct. You'll find yourself emptying the pan, hitting the tare button, letting the scale settle down, and then reweighing the charge. You'll also be grinding your teeth.
I still use my Gem Pro 250, but I start with a charge weight as close to the target as I can get. These days I use a Charge Master but I have also used a powder dipper and a mechanical charge thrower.
Once the charge is in the Gem Pro 250 pan, I remove the pan, shake the charge to center it up, and place the pan back on the scale because the Gem Pro will show the wrong weight if the charge isn't on center....... sigh. Then I use a tweezers to remove or add up to three kernels which weigh close to .02 gr each if you're using Varget or a similar powder. Then I dump the charge into the case.
If the initial charge is off by more than .06gr, I make an adjustment and re-weigh it, once again fine tuning by a kernel or two as necessary.
If you can come up with a way to hit your initial charge within .06gr of the ideal weight most of the time, the Gem Pro 250 isn't bad. If you can't, it's a real PITA especially if you try to use it with a conventional trickler.