Convert from zeptometer to button measure

Unit Definition (zeptometer)
The zeptometre (or zeptometer), symbol: zm, is an SI unit of metric length measurement. 1 zeptometre is 1e-21 metres, which is a very small distance

Unit Definition (button measure)
The button measure is a unit of distance equal to 1/40 inch (0.635 millimeter), used to measure the thickness of buttons.