You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?

When you weigh your body, an upward force acts on it. This upward force is the buoyant force. As a result, the body gets pushed slightly upwards, causing the weighing machine to show a reading less than the actual value. 

Our mass is more than 42 kg.

Even gases (like air) exert an upward force (or buoyant force) on the objects placed in them. Now, when we stand on a weighing machine, then the air exerts an upward force (buoyant force or upthrust) and makes us slightly lighter than we actually are. So, if a weighing machine shows our mass to be 42 kg, then our actual mass will be slightly more than 42 kg.