It takes significant effort to get in the groove of a particular 'day-to-day' math. My job has regularly recurring parts where I spend a lot of time doing one or more of 3 basic skills: setting up integrals and differential equations, converting lots of numbers to binary or hex, and trig-based approximations.

When I spend too much time away from one, it really shows. The other day, I tried to do the trig approximations, and it was like getting up after sitting too long with legs crossed. The fluency just wasn't there.