How do they match the weight of a prosthesis to the weight of the remaining breast?

My supplier measured me. I agree lopsided weight feels odd and also does your spine no good. Because of a persistent seroma, I had to wait a year for a proper prosthesis - took me a day or two to work out why I had some back ache after it was fitted!! It didn’t take long to rectify itself, more crazy that I didn’t realise it was happening. She also had a good range of suitable bras. Sorry, Melbourne based only. Good luck.