We all knew that velocity is time derivative of distance. So, I used simple mike and sound in 'Sound Velocity Based Temperature Measurement' as transmitter and receiver and enclose them at ends of 10 cm long test tube filled with dry air (except CO2). Then rest is the math velocity = (distance between transmitter and receiver/ time span took to travel sound between transmitter and receiver). As we know velocity of sound increases with increase in temperature. And with formula C = Co/(sqrt.(1+(temperature in degree Celsius/273))) I calculated the room temperature.