Maybe you should have read the link I posted...
Actually I did read the article. And I will grant you that in theory, it does make sense to use a check weight that is closer to your charge weight. However, I still stand by my statement that for the Fx120, it makes no difference whether you use a 50g or 100g weight. It all comes down to linearity.
In the article, they use the example of the EK-6000. This particular scale has a manufacturer linearity spec of
1 gram! That is three orders of magnitude (1000x) higher than the linearity of the Fx120. This means that your measurement can be off by as much as 15 grains, which of course is extremely dangerous for a reloader. So for this particular model, it is indeed important to calibrate with a weight close to your charge weight.
But this thread isn't about the EK-6000. We are talking about the Fx120, which has a linearity of 0.002g. That means that a calibrated scale is at most 0.002g off,
regardless of whether you use a 50g or 100g check weight. Maybe the 50g weight will give a slightly smaller bias for standard charge weights, but the
MAXIMUM possible bias is only 0.002g! That is roughly two granules of Retumbo powder.
Also, keep in mind that the average charge weight (let's say 40 grains) is still three orders of magnitude higher than the resolution of the scale. The bias will be the worst at the extreme ends of the weight range. Even a relatively light 40 grain weight is three orders of magnitude away from the extreme bottom end, thus it is reasonable to conclude that the actual bias in the 40 grain range is significantly less than 0.002g.
Bottom line, yes, you are right that a check weight closer to the charge weight is better. However, in practice, using the Fx120, the additional precision is completely useless since the bias is on the order of a single granule of powder.