Convert from spat to zeptometer

Unit Definition (spat)
The spat is an informal unit of distance formerly used by astronomers. The spat is equal to the terameter (Tm, or 10E12 meters). This is equivalent to about 6.6846 astronomical units. The origin of this usage is not clear; "spat" may be an acronym for "space unit" or "space-time".

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