What is this?
Aside from the Gregorian Calendar System there is a widely used
Persian Calendar
System also known as the
Jalali Calendar
System which Coda does not support. This doc has a simple solution for supporting Persian Calendar System alongside the native date.

It simply includes a table of 366 records (equivalent to the amount of days in a leap year), named
with auto generated columns (all formulas) mimicking the current Persian Calendar year (

Since its a simple Coda table, you can easily convert any Gregorian Calendar Date to any part of its equivalent Persian Calendar Date (or vice versa), using lookup or filter.

This solution is useful until Coda introduces a simple way of creating custom functions (e.g. using JavaScript) that could be used in formulas. Something like VBA scripts in Microsoft Excel.