1.16 Know and use the relationship between weight, mass and gravity

Weight = Mass x Gravity

YOUR WEIGHT IS NOT THE SAME AS YOUR MASS!

Your mass never changes - if your mass is 50 kg, you will still have a mass of 50 kg on the moon, on mars, anywhere. Your weight does change, because it is the effect of gravity on your body - this changes from planet to planet. And in space, of course, your weight = almost 0

W = M x G

Weight is a force, so it's measured in newtons. 
Mass ~ Kg
Gravity ~ 10 on Earth (units are mostly irrelevant, but if you really want to know, it's N/kg)

Fun fact, by Annabel:
The reason the unit for gravity is N/kg is because if you rearrange this equation so that gravity is the subject is becomes:
gravity = weight ÷ mass
which, in terms of units is gravity = N/kg