Circular index typewriters
The linear index had one great advantage over the square
index typewriter. It was the easiest and cheapest to produce. But working
on a linear index machine is tiring when you constantly need to shift
the index pointer over a distance of up to 8 inches.
The semi-circular index, like the American 2 and the World,
made life a bit easier. Instead of using the arm, a movement of the wrist
was now enough to select letters that were wide apart on the index strip.
The completely circular index went another step further.
Here all one usually had to do was turn a knob to select the right character.
Circular and semi-circular indexes were more widely used
than the linear index.