Comment by emergie

Consider a system with PID driver that samples temperature every 15-30min. Measures are not 100% regular, so we have to substract dates to calculate time duration between samples. Lets say we got one measure with timestamp 99-12-31 23:50 and second one with 00-01-01 00:15. What will calendar code do if we substract 99-12-31 23:50 from 00-01-01 00:15? Does 00y mean 2000 or 1900? What will the driver do when suddenly temperature differential will change without relation to physical reality?