1. n. 
A test procedure published by the API that specifies the use of a shearometer tube and a set of weights to measure the shear strength of a mud (lbf/100 ft2 or kPa). The typical use for this test is for evaluation of a static-aged mud sample left at high temperature for several hours. The shear tube is placed on the surface of the gelled mud and weights are applied until the tube sinks to a marked depth. The applied weight indicates shear strength of the mud sample.
Watkins TE and Nelson ME: "High Temperature Gellation of Drilling Fluids," Transactions of the AIME 193 (1953): 213-218.