I might also add that model in that picture is of a TDC that predates the impact angle dial. That dial shows lead angle in that model, it wasn’t until later models the impact angle was added, after that picture. Note the picture does not have the red impact angle lamp on it, that’s an indication that that dial did not indicate impact angle. The deal was changed to impact angle at the same time the red indicator light was added. And that indicator light lit up when the impact angle was less than 30 or greater than 150°.
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