The Three Pen Method of Self-Checking Work
File:PVE-1356, Date: Sept. 29, 2012, By:LRB
An irony of this computer era is that a code calculation and a drawing can be prepared by the same person on the same computer, but all the information on the drawing needs to be hand entered. In face of this lack of productivity, libraries of components or existing drawings get reused. Not updating all information in reused components is a leading cause of engineering errors.
Self-checking using the 3 pen method involves finding these errors by tracing program or drawing inputs back to the source document (a spec, a calculation or a sketch or drawing). Our work usually flows from original spec or sketch – to a calculation set – to a drawing. The calculation set is checked against the spec. The drawing is checked against the calculation set.
A printout of the calculation set is checked item by item against the source document. Drawing items are checked item by item against the calculation set. Items that are correct are highlighted in orange. Items that are not correct are circled in red. When finished it is easy to see the scope of what has been checked. It is also easy to see a glance what is wrong.
Finding mistakes in a document but failing to update all of them is very frustrating. This is avoided by highlighting the paper copy in green as the corrections are made on the computer. A quick check that all of the red marks have been highlighted in green indicates that all of the errors have been updated.
This self-checking method relies on using printed documents. For whatever reason, our experience is that this checking method works much better than any method we have tried that works on a computer screen.
For revisions, only the items that are changing need self-checking. The trick is to track items that are changing so that they can all be checked.
Self-checking is very good at finding incorrect data inputs in calculations or incorrect entries in drawings. Check lists are best to determine that items have not been missed… (A topic for another day.)
Material we use for our training class on self-checking is attached. We modified one of our sample vessel drawings to include a number of errors vs a calculation set. The attached drawing shows the items checked and found correct, found wrong, and items that have been updated. For this class there is only a drawing and a calculation set, so there is no original spec to also check against. A couple of checked pages from the calculation set are also enclosed.