A GENERAL-APPROACH TO COMPARISONS IN THE PRESENCE OF DRIFT

A general approach to comparisons in the presence of temporal drift is presented and comparison sequences are discussed for linear, quadrati c and cubic drift. Circular comparison sequences of the form (ab..)n a nd (ab..)(n)a are proposed (where a, b,.. are different items, such as masses, and n is a repeat factor) with the best performance achieved when three to five items are involved in the comparison. A matrix leas t squares model is used to obtain information about the drift, the ite m differences and their uncertainties. The emphasis of the paper is on mass comparisons, where the dominant drift is in the balance zero, bu t the approach is applicable to comparisons generally and its applicat ion to gain drift is also presented.