2Sten G A Bergmann. Nondestructive fild test of cement-grouted bolts with the boltometer[A]. In: Proc. of 5th Int. Cogr. Rock Mech.[C].Melbeoum: A.A. Balkema, 1983, 10-15
3Stephen C Tadolini. Evalution of ultrasonic measurement systems for bolt load determinations[R]. [s. l.]: Int. BU of Mines DGH PA29264,1990, 1-9