The Mackay Lacoste & Romberg G509 gravimeter is a very delicate instrument that makes physical (not electronic) measurements to a precision of 20 parts per billion, demonstrated in the field. It is a collaborative facility run and paid for by the Mackay PIs who use it. Because of the risk of damage and the benefits of prior experience to the data quality yielded, we only loan the Mackay Lacoste & Romberg G509 gravimeter to operators with sufficient prior experience, or to projects that employ an experienced operator for training project staff. John Louie will recommend experienced operators.