157 
Cleaning the gauge: All parts of the gauge should be carefully cleaned after 
each use. The metal parts should be oiled to prevent corrosion. Before re- 
usc, the gauge should again be cleaned to remove all the oil. 
Precautions: When the Hilliar gauge fails to function, it is nearly always 
due to water leaking into the gauge. If leaks occur any information obtained 
is unreliable. The instruction found herein is designed not only to assist 
in the proper assembling of the gauge but also to assure that the gauge after 
assembly will be and remain watertight until subjected to a shock wave. 
Thin layers of cement often cling to the bottom of the pellets, This 
layer and other dirt should be removed before the disks are measured. 
