I keep my measurement within an inch of my leanest number, which is around 31 inches. If you're not pigging out and retaining lots of water, you'll see a true measurement early in the morning -- and when you're lean, the incremental changes will be small. So if you want to panic about getting fatter, do it when the amount of inches has gone up too much for your own tastes.
When it comes to leaning/bulking, I kind of do both at the same time. While officially "cutting" -- which I've been doing since early in June --- I have little cycles where I hit the weights harder and eat a little more. I feel like when noticeable progress has been made with dropping fat, and I'm seeing more definition and vascularity, that's when I take a step back and go into maintenance phase for couple of weeks, to reset hormones and mental state. While I do like eating for leanness, I would be lying if I said I didn't like eating more. The goal is to not gain or lose at this stage, although I have become leaner during maintenance phases which is probably carry-over from my metabolism firing on all cylinders.
So after that mini-maintenance phase, I go back into eating cleaner (and less) to drop some more fat. And I take my time. This summer I retained almost all the muscle I gained because I didn't do ridiculous amounts of cardio, nor did I starve myself, and I was also in no rush.
When I go into a muscle building phase (I don't call it bulking) at the end of summer, I'll do the reverse of what I just described. Calories will be added, I'll go for more volume(especially deadlifting) and take a break occasionally to trim some fat.
This two steps forward, one step back approach has been working so well for me -- as opposed to spending long amounts of time "cutting" or "bulking". Overall, the goal is to never get fat and stay more ripped than the average dude all year round. No more of this getting fat during the winter bullshit.