physics about moment and force

Let the length of left arm be l1 and length of right arm be l2 and the unknown mass has mass M.
An unknown mass is weighed first on the left pan. It gives reading X.
Taking moment => Ml1=Xl2 --- (1)
and then on the right pan. It gives reading Y.
Taking moment => Yl1=Ml2 --- (2)
(1) / (2) gives
M/Y = X / M
M2 = XY
M = square root of (XY)