A list of differencing lags can be placed in parentheses after the variable name to request that the series be differenced at these lags. For example, VAR=X(1) takes the first differences of X.

Recently, a study introduced a novel method that significantly enhances the precision and efficiency of precise orbit determination and clock estimation the Global Positioning System (GPS), BeiDou ...

Keidai Iiyama, Sriramya Bhamidipati and Grace Gao, “Precise Positioning and Timekeeping in a Lunar Orbit via Terrestrial GPS Time-Differenced Carrier-Phase Measurements.” Satellite Ephemeris ...