Calculating SWR with RF directional couplers

[anatolyk69_gmail.c]

^ is power (mathematical, not electrical ), according to: http://www.cplusplus.com/reference/cmath/pow/
Power = pow(( Volts / 0.281 ), 2); may works, or
Power = ( Volts / 0.281 ) * ( Volts / 0.281 );