you take the weight you want to lose, pack it into a backpack and walk around with it for a while and then take it off - that would give you a really good idea of how much lighter you will feel having lost the weight
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LOL. When I told DH that I wanted to lose 30kg, he immediately said "That is three full watering cans of water" (a weight I am familiar with from watering all his homegrown tomatoes, LOL!)