The calibration balance of the Brotherhood of St. Eloy has a wooden column with a quadrangular section, bearing a plaque showing a few inscriptions. The 2 pans were initially suspended by strings made of green twisted silk. It sits inside a wooden cabinet with diamond-patterned glass doors. The cabinet measures are 1.60 x 0.66 x 2.90 m and it has 3 iron locks. The section below has doors where the weights are kept.

The balance was described in the inventory of January 5, 1788: “One arm of the large balance bearing a label inscribed with silver letters, brass pans and green silk strings, and with two rests made of Pau-Brazil with its golden-brass rings that are for putting under the pans.“