By a straightforward calculation,
LSS = 38.94 x sqr( temp )
WHERE :
LSS = local speed of sound ( knots )
temp = Ambient temperature in degrees Kelvin
sqr = square root function
OR
put the ambient temperature on the inner bit of your whizz wheel against the mach index mark, then read off LSS ( in knots ) as required. LSS is related ONLY to ambient temperature.
Conversions between knots and kmh are also a piece of piss on the whizz wheel.