I've started to use the Log-Normal distribution for estimation. Because I think of development like planning a travel time, the train will either arrive in time

I've started to use the Log-Normal distribution for estimation. Because I think of development like planning a travel time, the train will either arrive in time or the will be a random amount of interruptions/errors that add up. But there won't be as much stuff that speeds the train up (wins back some time). Then I try to communicate the distribution in words or show it, which most often has a hard time to be accepted, because managers expect a normal distribution mean. I let several people estimate large scale features and keep their variance to feed it into the log normal. Often I use a reference project, let the use smaller numbers (but not Fibonacci numbers [1]) to estimate and calculate it back to work days. [1] I personally think the Planning Poker numbers are a lay man's way to force a Log-Normal distribution in the estimation