ISA FL330 = +15º - (2º x 33) = +15º - 66º = -51ºC deviation = +15ºC, OAT = -36ºC.  

In the AIRSPEED window put the temperature (-36ºC) next to the Mach No Index, go to the TAS (487kts) on the outer main scale and read the Mach No next to it; 0.81.