Since the formula for the shaped charge jet break-up time was published on 1979 many attempts were made to interpret it and to make its use more efficient. It is shown herein that the V-pl parameter depends on the ratio of the liner thickness to the charge explosive diameter by the formula: 1/V-pl=13.9-101 . (T-L/CD), where T-L is the liner thickness, CD is the explosive charge diameter and the numbers are for a published set of measurements with an OFE copper liner driven by COMP-B explosive. To find how the numbers used in this formula change with the liner material and its metallurgical state and with the type of explosive, measurements should be made as prescribed herein. An attempt to begin explaining this formula is made in the discussion.