train was apparent on graphic records only for shots with yields of 1.7 Mt and greater; also, the greater detection ranges, the larger numbers of stations recording, and the generally higher amplitude all were indicative of larger shots. 7.2.6 Directional Effects. The shift noted in travel speeds (speeds toward the east greater than that toward the west in March shifting to the opposite in May) were consis- tent with previous observations. for stratosphere winds. This indicates that April was the change-over month 7.2.7 Equipment. Standard equipment was superior to VLF equipment for detection purposes and provided a convenient, though inaccurate, means of estimating yield. In addition, most standard recordings showed some evidence of the dispersive train, though with greatly reduced amplitude at the longer periods. Jt remains to be seen whether VLF recordings of the longer periods will give an accurate estimate of yield. 7.3 ANALYSIS OF NUCLEAR-DEVICE DEBRIS 98