<Tr> <Td> 25101 / 850 </Td> <Td> Not accurate due to the multi-millenial change of the synodic month length . </Td> </Tr> <P> These fractions can be used to construct a lunar calendar, or in combination with a solar calendar to produce a lunisolar calendar . A 49 month cycle was proposed as the basis of an alternative Easter computation by Isaac Newton around 1700 . The tabular Islamic calendar's 360 month cycle is equivalent to 24 × 15 months, minus a correction of one day . </P>

Who calculated the duration of a year and the lunar phases