Linear compensation = (Thermal Coefficient of Expansion) X (Displacement + Change in Temperature of Each Axis and the Part). If multiple temperature sensors exist on an axis, PC-DMIS averages the readouts to find the temperature change.
Structural compensation recognizes that a CMM's various material components may have different temperatures (a single axis of the machine, for example, may have several different temperatures, which cause bending, bowing or skewing of the machine in some way). Structural compensation, then, applies the temperature corrections for specific areas of the CMM. When you select Edit | Preferences | Temperature Compensation Setup, the Structural Thermal_OCX gets called, and PC-DMIS calculates a new temporary volumetric compensation map.