There's a lot that's just unpredictable. Some cats get more predictable #s than others, a lot of times you just never know for sure what the reasons are for #s being different day to day. Like others said it's always useful to have mid-cycle #s, otherwise it's just a guess. There are bounces from the #s going too low or the drop being too steep, in which case you need to reduce the dose, and bounces from liver training (#s not too low & drop not too steep, but #s they aren't used to so they freak out), in which case you want to hold the dose steady through the bounce, and then after that evaluate whether you are at the right dose, or need an increase. Without mid-cycle data, it's just guesswork what happened. And of course there are explanations other than bounces too - snuck some dry food, cat fight outside got them riled up, etc.