Shallow seismic reflection survey

An adjustable finger ring having two tubular pivoted sections, one having a slot with a transverse catch pin and the second pivoted section having an arcuate spring slidably engaged in the first pivoted section and an arcuate notched latch receivable in the slot and lockingly engageable with the transverse catch pin. The inner end of the latch has a tooth engaged in an aperture in the spring, and the spring is channelled to receive the inner end of the latch. The interengaged inner end portions of the latch and spring are telescopically received in the second pivoted section and the inner end of the spring is fastened to the second pivoted section by a pin.