A friend of mine said this today:

I’ve also been mulling the idea of tracking cognitive ‘stack depth’ levels throughout the day. The idea is simple: if you were working on A, then interrupted to deal with B, and while attending to B were interrupted with a question about C, then you attained a maximum CSD of 3. My theory is that if the MCSD exceeds some fixed amount on a fairly regular basis, one’s productivity falls dramatically. It seems to me that I occasionally hit values of 4 or 5…

I think he is absolutely right about this. What do you think?