I'm far from a mathematician, but the field I'm trying to break into (management consulting) requires a fair amount of mental arithmetic. I'm okay, but I'm not even close to as good as I need to be in terms of both speed and accuracy.
I have math apps on my iPhone. I use online mental math tools. I try to do mental when I'm just sitting around. Anyhow, I've been noticing that I'm not getting better. In fact I'm making more mistakes and it seems like I'm struggling more to get answers.
I suspect that I may be pushing it too hard. Right now I'm doing all four major operations in sets of 50 and 100, and taking times tests multiple times per day. After it all sometimes my brain just hurts. Nevertheless I push on because the old adage with math is "practice, practice, practice."
Yet, I'm curious -- is there decreasing returns in speed and accuracy to more mental math practice? If I push through another set of hundred basic questions at 2:00 am before I go to bed -- am I helping myself productivity or hurting it?