Of course to measure out 42 litres from two jugs of 5 and 17 litres each on the day that the Sun is in the exact same position among the constellations as today, and so is the Moon and in the same phase.

I thought this was obvious, like which is the better editor vi or whatever that other one was.

More here

https://web.archive.org/web/20160615205452/http://www2.slgb.... Section 2

https://hal.science/hal-01254966v1/file/MayaEnigma.pdf

https://www.ias.ac.in/article/fulltext/reso/007/10/0006-0022