Are all those “tricks” that force you to memorize a bunch of nonsensical rules really easier than just remembering that 1st of January 1900 was a Monday.
And you just move it up the same amount of days as the remainder of (Amount of years ) + (Amount of leap years which is just amount of years since 1900 divided by 4) +(amount of days passed in the year minus 1) divided by 7.
Sure you might be calculating a while in your head. But at least you don’t have to memorize a whole bunch of series.
For example, 15th of February 1987.
Years since 1900 = 87
Leap years since 1900 = 87 / 4 = 21
Day of the year (everyone knows how many days in each month, and it’s not that hard to quickly calculate that) = 46 – 1 =45
87 + 21 + 45 = 153
Remainder of 153 / 7 is 6
15th of February 1987 was a Sunday