I have just remembered the sequence.
In 1962 we were issued coloured wooden chronograph lead pencils. These were just coloured pencils but the lead was chinagraph. They were sharpened the same was as a lead pencil with wood shavings into the pencil box and of course a sharp point that soon flattened. The aircraft was not particularly hot so the lead would become brittle and break.
The leap forward was the self sharpening pencil. This was a tightly bound material with a cotton thread IIRC which you pulled, the binding would unwind and a new lead would be available.
Then came ubiquitous plastic models.