Use fixed year of 365 days
From https://discuss.tryton.org/t/linear-depreciation-for-10-years-is-not-10/1860
When asset starts or ends on a leap year, the rate used for full year may seem strange for a multiple of year range because there may be 1 or 2 days more which change the angle of the line a little bit.
I think to avoid incomprehension and astonishment, it will be better to always compute rate using fixed year of 365 days (by ignoring all the 29/2 days).