When selecting the initial sources (up to about 3/4 of the total) in a geodetic sequence, SCHED tries to find one that are especially low or high at some stations. GEOLOWEL sets the upper bound of the region considered to be low. OPMINEL sets the lower bound. The related parameter GEOHIEL sets the lower bound to the ``high'' region. The default GEOLOWEL of 23 degrees has a SecZ of 2.55 which differs by 1.0 from the SecZ of 40 degrees, the default for GEOHIEL.