mach ?
Hello Alex,
there is a formula : EAS = 661xMxroot of greek letter delta
delta= pressure ratio P/Po
at fl100 P= 700hpa(see wx charts)
at sea level Po=1013hpa
700/1013=0,69 => square root= 0,83
CAS~EAS( difference= compressibility error)
661kt is speed of sound at sl std
so finally as an approximate ; 230kt=661xMx0,83
I let you work out the Mach number