I was playing around with retractable blades and noticed a miscalculation for the weight. The rules (quoted below), calculate the weight at Mech tonnage / 20, rounded up to nearest half ton, PLUS an extra half ton for the mechanism itself.
For example, the weight of a retractable blade for a 50 ton mech should be 3 tons (50 tons/20 = 2.5, plus another 0.5 for the mechanism = 3 tons). The site calculates it at 2.5.
I've tested a bunch of mechs of different tonnage classes and it all comes out the same - the extra half ton weight for the mechanism doesn't seem to be included in the calculation. The number of critical slots and damage totals are correct, it's just the tonnage that's off.