How many types of pellet are in general use? Two? 8.4 and 7.9 grain.
So how about before a shoot, the chrono marshals weigh out some stock pellets and ensure they are whatever weight is specified on the tin. They can also check that the skirts are in good condition.........
When you arrive you say, I am shooting 8.4 grain, they load your gun with one of their pre-weighed pellets and test fire it.
Now the digital scales can be checked indoors against a reference weight, the better ones come with a calibration weight anyway, so you know the pellets are the specified weight and that has some traceability. It also takes out of the equation the huge errors arising from weighing pellets in the field.
For those who shoot Bismags or Barracudas then include 10.5 if you wish.