In the production of plastics, the plastication unit or "barrel" has the task of melting the plastic "shot" material and then inserting the molten plastic into the mould, where it will then cool and form some useful product. Barrel residence time is how long it takes the shot to go from entering the plastication unit to leaving out the nozzle to the mould. Excessive barrel residence time can lead to material weakness and subsequent degradation of the finished plastic product.

Multiply "M" by two if "L" is less than four. Multiply "M" by 1.4 if "L" is greater than or equal to four. For example, if "M" is 200 grams and "L" is four, the result is 280.

Divide the result by "S." For example, 280 divided by 100 grams is 2.8.

Multiply the result by "C." For example, 2.8 times 15 seconds yields 42. Under these conditions, the barrel residence time is 42 seconds.