A float lifts Mazarine 1 meter, so it is +1. A weight pulls her down 1 meter, so it is −1. The sign of the second number tells you which pieces. Plus between the numbers means you clamp them on (adding). Minus means you cut them loose (subtracting).
Example
What happens
Result
5 + 3 = 8
clamp on 3 floats
she rises 3
5 + (−3) = 2
clamp on 3 weights
she sinks 3
5 − 3 = 2
cut loose 3 floats
she sinks 3
5 − (−3) = 8
cut loose 3 weights
she rises 3
Look at the last row. When she cuts weights loose, nothing is added to her, but something heavy leaves, so she rises. That is why subtracting a negative number is the same as adding a positive one.
You can only cut loose what is already on the hull. When there is not enough, clamp on zero pairs first: one float and one weight together, +1 and −1, which make 0. Her level does not change, and now there is something to cut loose.