I red an interesting view about a programmer’s estimating abilities :

An experienced project manager I used to work with claimed that he took the programmers’ time estimates, multiplied by pi and converted to the next time magnitude to get the true number. 1 day converts to 3.14 weeks. He had learned the hard way that programmers are bad at estimating times. To get a more precise conversion, I’ve created a translation table for programmers’ time estimations, trying to narrow down where things go wrong.

 

 

Read more here : http://architects.dzone.com/programmers-are-bad-estimating