There already are algorithms that can be used to concert a date from different calendars into the Julian Day Number (JDN) and a JDN into the Hebrew calendar.
But how can one calculate the conversion from JDN to the Hebrew calendar in the old fashioned way, for all practical purposes only with a pen and paper? What would be the computational steps necessary, when one can only use +, -, *, /, modulo, and rounding?
If the JDN to Hebrew calendar conversion is too complex, is there a different calendar that could be used as a source which would allow an easier calculation?