The lever tapers from 1-1/2 inches at the pivot to 5/8 inch at the balance end.  The hole for the pivot—­5/16-inch steel bar—­should be long enough to admit a piece of tubing fitting the bar, to diminish friction, and an important point, be drilled near the handle edge of the lever, so as to leave plenty of wood to take the strain.  The last remark also applies to the hole for the balance pin at Q.

The balance support, B, and the pivot piece, C, are 2-1/2 and 2-7/16 inches high respectively.  Run a hole vertically through C and the baseboard for the pivot, which should be 4-1/2 inches long, so as to project 1 inch when driven right home.  Take some trouble over getting the holes in L and C quite square to the baseboard, as any inaccuracy will make the lever twist as it moves.  To prevent the pivot cutting into the wood, screw to the top of C a brass plate bored to fit the pivot accurately.  The strain will then be shared by the screws.

The horns of A should be long enough to allow the outside of the fixed grip to be 2-1/4 inches from the inside of the handle.

The balance is secured first to the lever by a pin driven through the eye of the hook, and then to B by a 3-inch screw passed through the ring.  The balance should just not be in tension.

When the apparatus is so far complete, test it by means of a second balance applied to D. Set the scale-marker at zero, and pull on the D balance till, say, 35 lbs. is attained.  If the fixed balance shows 7 lbs. on what is meant to be a 5 to 1 ratio, the setting of R relatively to P and Q is correct.  If, however, there is a serious discrepancy, it would be worth while making tests with a very strong balance, and establishing a corrected gradation on a paper dial pasted to the face of E.

For twisting tests we need a special handle (see Fig. 164), which is slipped on to the pivot and transmits the twist to L through a pin pressing on the back of the lever.  The stirrup is made out of strip iron, bent to shape and drilled near the ends for the grip spindle.  To the bottom is screwed and soldered a brass or iron plate, into the underside of which the pin is driven.

[Illustration:  Fig. 164.—­Handle for twisting test.]

To prevent the handle bending over, solder round the pivot hole 3/4 inch of brass tubing, fitting the pivot closely.

Tests.—­Grip tests should be made with each hand separately.  The baseboard should lie flat on a table or other convenient support, and be steadied, but not pushed, by the hand not gripping.

Twisting tests may be made inwards with the right hand, and back-handedly with the left.  The apparatus is stood on edge, square to the performer, resting on the horns of A and a support near the balance.

Finger tests are made by placing the thumb on the front face of B, and two fingers on the farther side of the lever, one to the left and the other to the right of the tail of the balance.