Drawing Pens

[DYER,SONIA (HP-Cupertino,ex1)]

Timo wrote:
>Anyway they used more or less pen like this for inking:
>http://www.geocities.com/timoro2/pen.html
>Steel tip dipped in bottle of ink. For penciling most often used pen was 
>blue pencil.

   I know how easy it is to accidently make a blob or a smear with that kind
of pen.  How did they make corrections back in those days before correction
fluid and felt-tip pens became common?  Did they have to start the drawing
over?

		Sonia