The Self Temperature Compensation (STC) value seeks to minimize the "apparent strain" (change in gage resistance caused by temperature change at the gage site) as opposed to change in gage resistance do to mechanical load on the test piece.  If your testing program will be conducted under essentially constant temperature conditions, this error in reported mechanical strain is negligible and you should select STC=11 ppm/deg C for best gage availability from factory stock. If temperature conditions are variable during testing, choose the STC value closest to the Thermal Coefficient of Expansion (TCE) of the material on which the gage will be mounted.
                             Select STC Value