Draught dynamometer by Cottam and Hallen. Simply an elliptical spring, which, in proportion to the longitudinal extension suffered when in use, experiences a lateral collapse, the measure of which indicates the amount of strain to which it has been subjected.

A dynamometer is an instrument for determining the force required for the work done, which in the case of the plough was measured by the strain upon the draught chain. To achieve this, the dynamometer was made a link in the draught chain and subjected to the necessary tension.

The use of the dynamometer resulted in greater precision in the comparison of draught under the same soil conditions, and was extremely useful in determining the relative merits of the ploughs at the many trials held during the 19th century. The first dynamometer appears to have been invented about 1770 by Mr. Samuel More, the Secretary to the Society of Arts. It was used in the ploughing trials help by the Society in 1773.

Travelling case for draught dynamometer by Cottam and Hallen.