count the number of days since the last start of a month (knowing that the length of the lunar month is 29 or 30 days); given that the length of the synodic lunar month is not a multiple of days and can even vary from 29.26 to 29.80 days, this can introduce an error source of $\pm 1$ day. Alternatively, one can observe the moon later and determine its age or phase. With the latter method, one can correct the start of the month and the current date (inside a lunar month) any time during the month. However, the precision of this method is also not perfect, but has an error of at least $\pm 1$ day, if not $\pm 2$ days. In addition, some $15~\%$ of claimed lunar crescent sightings even by experienced observers can be wrong, e.g. being reported several hours too early (Doggett & Schaefer 1994). Hence, without a calibration point in the given month (e.g. an independent dating by a different source in a different calendar or a weekday mentioned together with a date), any conversion between a Muslim date and a Julian/Gregorian date has an error of $\pm 1$ day ($\sim 1 \sigma$ error bar), 