I was out in the shop today to reload some .38 Special. Being a cautious reloader, I wanted to verify my charge weights before I began cranking out ammo, so I set up my Hornady scale to verify the weight of powder that my measure was throwing.
The scale was hard to zero, and I finally realized that a fan across the shop was effecting the balance beam. Those gentle air currents were playing hob with my scale, as this video documents.
Of course, I turned the fan off, verified my weights, then turned the fan back on to load the ammo.
But, even advanced reloaders can benefit from reviewing the basics.