The Perth Sand Penetrometer (PSP) is widely used in WA for compaction control, particularly for preparation of sand foundations for domestic and light commercial structures. The relevant Australian Standard (AS12126.96.36.199–1997) specifies that the test is to be performed by first inserting the penetrometer to a depth of 150 mm below the ground surface, and then counting the number of blows required to achieve a further 300 mm penetration (to a total penetration depth of 450 mm). In practice the test can be, and frequently is, continued to greater depths – typically for another 300 mm (to a depth of 750 mm), but sometimes to even greater depths. However, there is contradictory evidence of how the increase in test depth affects the measured blowcounts for a given constant relative density with depth. This paper presents the results of some studies into this effect. It is concluded that there is no definitive universal relationship between blowcounts and depth for any given relative density, and hence site-specific calibration would be required if the test was to be used in this manner for any important project.