This comes from Cap 768 Guidance to operators.
3.2 Prevailing visibility encountered could be significantly less than that reported.
Prevailing visibility alone is forecast or reported unless the minimum visibility (in any
sector of the aerodrome) is less than 50% of that prevailing or below 1500 metres
(whichever is worse). In those circumstances, a minimum visibility value and direction
is given in addition to the prevailing visibility. When two visibilities are given, the lower
figure should be used for operational decisions if it could affect the aircraft's approach
to land.
Spitoon - I have encountered that many times but it is reported as MIFG.