Average page load time incoherence

Hello all,
the average page load time is supposed to be the sum of all previous metrics listed, but it is always lower (we can see differences between the “total” displayed when we move the mouse on the graph and the value in the global performance table below). Can anybody explain it ?
I’m trying to get the correct value of average page load time for a whole site on a monthly basis.

Hi @Yomghi
This is probably due to some roundings…