860 
This may change the pressure behind a viston by a few percent, 
since a piston may recoil with high velocity. Cavitation and 
turbulence are shown to be unimportant in present gauges. The 
important affects, namely, recoil of pistons, recoil of block, 
and Bernovili effect can be corrected, except for an uncertainty 
of about 2% in the pressure provided that the gauge ise used in the 
head-on position. It is thus theoretically vreferable to use a 
gauge in this position. If, for any reason, however, a gauge 
is used in the side-on position, it may be calibrated egainst a 
head-on gauge. 
ES 0 a 
