minor fix

production.py

@@ -91,11 +91,11 @@ class Production(metaclass=PoolMeta):
         return new_cost_price
 
     def get_perfomance(self):
-        res = 0
+        res = Decimal(0)
         origin = sum(p.quantity for p in self.bom.outputs )
         result = sum(p.quantity for p in self.outputs)
         if result != 0 and origin != 0:
-            res = result/origin
+            res = Decimal(str(round(result/origin), 2))
         return res
 
     def update_product_cost(self, product):