Weighty

Every week I have to check the accuracy of the balances in our lab. Every year the balances need recalibrating and every two years the weights I use to check them need recalibrating too.

Doing this isn't really very exciting but I do love the beautiful weights in their little red velvet boxes. These weights are 100g, 20g and 1g and the little fleck of metal at the front is 1mg or 1/1000 of a gram.

How they are able to check the weights accurately I am not sure since I am not sure how you calibrate the weights you are using to calibrate. I know The Kilogram lives in France, is known as the International Prototype Kilogram and is kept under constant conditions. Replicas have been made against which other countries may send their kilograms to be checked - the original weight is too precious to be constantly used as exposure to the air will add contaminants and thus weight.. However these replica weights have drifted in comparison to it, due to picking up these contaminants. Or possibly the IPK itself has changed in weight itself and got lighter. It is difficult to tell which has changed relative to one another!