Recent development of a system of gravity measurement in an airplane requires the determination of gravity values in the air from ground surveys to provide values with which airborne values can be compared. Calculation of such values involves an upward continuation operation. A test of the several published continuation systems was carried out by applying them to 2 theoretical doubly periodic fields for which a theoretically continued value can be calculated. An important consideration is to determine a minimum practical value for R/h, or the ratio of the radius of the field covered to the height of continuation, as this ratio determines the width of the belt of ground data required to calculate comparison data for a test flight line. From tests of continuation coefficients by Peters, by Henderson, and by Tsuboi with various values for R/h, the minimum R/h value is indicated to be about 6. Consideration is given to the "truncation" error which results from the necessarily finite limit of the field of calculation. No clear preference for the different empirical treatments of this error can be made on theoretical grounds, but an arbitrary adjustment to make the coefficients sum to unity is not required.