Most users of progressives, don't totally rely on the machine either. I look visually, as well as using the powder alarm on the Dillon 650. During the process of reloads, I'll also periodically check the powder measure against my electronic & balance scales.

With mass produced loads, I'm not going for exact matched cartridges, where bullet weight & powder weight need to be exactly the same. Just as with factory made ammo, I expect chrono results to vary somewhat.