Abstract: Apparatus for determining compressive stress in an in-situ roof support pillar may comprise a convergence meter positioned in one of the two entries for measuring the total entry convergence, i.e., roof sag and floor heave, and for generating an output signal related thereto. A computer system connected to the convergence meter is responsive to the output signal and calculates the compressive stress in the pillar based on the total entry convergence and based on whether the pillar is being subjected to at least one of a number of load types including a first front abutment load, a second front abutment load, and a side abutment load.