tigger:
Brilliant library
I've been sweating blood trying to get the daylight saving rules to work in Excel prior to transferring to code and getting nowhere fast.
I have an energy monitoring programme that counts the meter (gas, electricity etc.) pulses that puts the RTC (GMT) time/date-stamp on it and for clarity needed the local time/date as well.
Saved me a lot of midnight oil, especially galling as I just found I installed the library last year.
I will get the Excel version going for personal satisfaction, but the rules to compare the system date/time against the changeover date/time are a lot harder than they appear.
Personally speaking, I'm in favour of leaving the damn clocks alone, as "putting the clocks back" in October just brings the gloom on one hour earlier.
Here is one method, which probably would not be too hard to make work in Excel:
https://forum.arduino.cc/index.php?topic=370460.msg2554547#msg2554547