Between these nails a fine wire is stretched free of the beam and kept taut by means of a rubber band or coiled spring on one end.
Behind the wire at a point on the beam midway between the supports a steel scale graduated to hundredths of an inch is fastened vertically by means of thumb-tacks or small screws passing through holes in it.

Attachment should be made on the neutral plane.
The first reading is made when the scale beam is balanced at zero load, and afterward at regular increments of the load which is applied continuously and at a uniform speed.

(See SPEED OF TESTING MACHINE, above.) If desired, however, the load may be read at regular increments of deflection.

The deflection readings should be to the nearest 0.01 inch.

To avoid error due to parallax, the readings may be taken by means of a reading telescope about ten feet distant and approximately on a level with the wire.