In parsha Balak (Bamidbar 22:6) we are told of how Balak hired Bilam to curse the Jews. How could a man like Bilam curse the Jews? The Gemara explains that it was because Bilam knew the moment each day…..The Gemara says that there is a moment each day that Hashem becomes angry at the evil doers of the world. (Berachos 7a) Rabbeinu Tam sites a Tosefta that quantifies the lenght of this moment, called a rega. A rega is 1/24 of an eis. An eis is 1/24 of an onah. An onah is 1/24 of a sha’ah. A sha’ah is 1/24 of the day (i.e. one hour).
What fraction of a sha’ah is a rega?
1/24 x 1/24 x 1/24 = 1/13,824 of a sha’ah
If a sha’ah is 60 minutes what fraction of a second is a rega?
Number of seconds in a hour = 60 x 60 = 3,600
Number of rega’im in an hour = 13,824
3,600 / 13,824 = 25/96 of a second