learn to judge of proper proportion and relation of parts, especially as
we have no convenient tool for measuring the angular motion of the fork
or escape wheel. Nor is it important that we should have, if the workman
is thoroughly "booked up" in the principles involved.

As we explained early in this treatise, there is no imperative necessity
compelling us to have the pallets and fork move through ten degrees any
more than nine and one-half degrees, except that experience has proven
that ten degrees is about the right thing for good results. In this day,
when such a large percentage of lever escapements have exposed pallets,
we can very readily manipulate the pallets to match the fork and roller
action. For that matter, in many instances, with a faulty lever
escapement, the best way to go about putting it to rights is to first
set the fork and roller so they act correctly, and then bring the
pallets to conform to the angular motion of the fork so adjusted.


FORK AND ROLLER ACTION.

Although we could say a good deal more about pallets and pallet action,
still we think it advisable to drop for the present this particular part
of the lever escapement and take up fork and roller action, because, as
we have stated, frequently the fork and roller are principally at fault.
In considering the action and relation of the parts of the fork and
roller, we will first define what is considered necessary to constitute
a good, sound construction where the fork vibrates through ten degrees
of angular motion and is supposed to be engaged with the roller by means
of the jewel pin for thirty degrees of angular motion of the balance.

There is no special reason why thirty degrees of roller action should be