For the on going assembly item Component ID No. 494, what's the Unit measure for it?
On going assembly item means the assembly item haven't been finished, therefore EndDate is null
SELECT T2.Name FROM BillOfMaterials AS T1 INNER JOIN UnitMeasure AS T2 ON T1.UnitMeasureCode = T2.UnitMeasureCode WHERE T1.ComponentID = 494 AND T1.EndDate IS NULL GROUP BY T2.name