The etching folds up to make a jig in which a fine strip of plasticard is placed. This is then positioned in line with the door centre. A drop of solvent will then bond it to the roof of the vehicle, in the correct position. This will ensure correct and consistent positioning of these prominent features. Click on the photograph to see a detailed picture of its use.
For shorter srips, as used by the Southern Railway. Attach only the centre of the strip very sparingly, and remove the jig. Trim the strip to length, pulling down the ends to get the shape right.