So TechManual states that Clan MASC (pg. 51) is 4% of the BattleMech's total weight in tons (and crits), and "Round this figure normally to the nearest full ton/critical slot."

This works for standard Mech designs, but then TacOps comes around with its Ultra-Light BattleMech designs and things get wonky.

10 ton Mech, 4% of its weight is 0.4 tons, rounded normally...to 0 tons. And 0 slots.

So it probably isn't supposed to work out that 10 ton BattleMechs can get a 0 ton/0 Critical slot Clan MASC. (or maybe it is).

So if not, how should his be resolved?

The footnote states "Round this figure normally to the nearest full ton/critical slot."

Should we assume that "nearest full ton" means it has to weigh atleast one ton, and thus despite normally rounding 0.4 down, we have to round up in this case? If so, this would put Clan MASC and IS MASC at the same tonnage/crit.

Should it be something else? Maybe errata for the Ultra-Light BattleMech section TacOps (Advanced Weapons and Equipment, page 190), stating that Clan MASC should be 0.5 tons/1 crit for 10 ton Mechs?

So. 10 ton mech. 4% equal 0.4 tons.

Does it go to 1 ton. 0 tons, or something else?