Abstract: An affinity type gravity measurement instrument which is composed of material such as wood having a coefficient of thermal expansion. Within an internal cavity defined within the housing is disposed a quantity of liquid and a float partially submerged in the liquid. The liquid and float have low coefficients of thermal expansion. The housing defines an internal temperature compensation cavity receiving liquid upon expansion thereof to thus minimize change in the height of the liquid column and thus change in the position of the float and target response to temperature change. A stem of the float extends through an opening at the upper portion of the housing and supports a target, the position of which is sensed by an eddy current, laser or radar proximity sensor, developing signals which are processed for digital readout and computer processed for mapping.