Question: what is the primary difference between the pen tool and the pencil tool

title: Technical drawing tool
text: A drafting machine is a device which is mounted to the drawing board . It has rulers whose angles can be precisely adjusted with a controlling mechanism . There are two main types of apparatus : an arm - type parallelogram apparatus based on a hinged arm ; and a track - type apparatus which moves on a rail mounted to the top of the drawing board . The accuracy of the arm type apparatus is better in the middle of the board , decreasing towards the edges , whereas a track machine has a constant accuracy over the whole board . The drawing head of a track - type drafting machine slides on bearings in a vertical rail , which in turn is moved along a horizontal , top - mounted rail . Both apparatus types have an adjustable drawing - head with rules attached to a protractor scale so that the angle of the rules may be adjusted .