Template:Perseverance Mission Timer/doc

Usage
Usage for a (UTC) time in the past (difference in sols between NASA-defined Perseverance rover mission beginning and given date): For current time, simply use:

Calculation basis
Perseverance mission clock according to the official NASA Perseverance mission timer: 
 * the NASA Mars Clock (at https://mars.nasa.gov/mars2020/) and the "MARS24" program (at http://www.giss.nasa.gov/tools/mars24/) are not "official" NASA Mars Clocks, may give similar times and may be "off by some odd amount" (by "1 or 2 seconds" at last look?) from the true official Mars Clock "kernel" - (the "official 'kernel' [is] maintained at JPL").
 * the "Perseverance mission clock starts from mean local solar midnight immediately preceding touchdown, and for the midnight at the originally planned landing longitude and not the actual landing longitude. As Mars2020 touched down mid afternoon local time, a clock started at the time of touchdown would lag between the mission clock by about 15 Mars hours." [use SpaceCraft Event Time (SCET) rather than Earth Received Time (ERT) which may be "off by about 14 minutes"].
 * in summary, "if you plug the time and date UT 2021-02-18 13:50:00 into an Mars2020 timekeeping calculation, you should obtain that it is mission time 00:00 on Sol 0. If you're off by a second or two, you're doing as well as Mars24. If you're off by about 7-8 seconds, you may be using the landing longitude in the calculation rather than the planned longitude. If you're off by about 14 minutes, then you probably have ERT rather than SCET."