The BOF-EX is an incremental borehole extensometer. This design of extensometer is extremely stable and accurate. Unlike rod-type extensometer (MPBX), the 32 mm OD rigid tubing sections eliminate possible bending and friction between rods, and thermal effect is significantly reduced as each measuring module is placed inside the borehole next to the anchor.

Datasheet: 

BOFEX-E5004C-060501.pdf

Manual: 

E1004C-080918_BOF-EX Retrievable Borehole.pdf