A gauge system , the gauge system comprising: a frame ; means for securing the frame to an interior surface of an annular shape that has an axis and a circumferential direction, the securing means comprising multiple units that extend in an outward direction from the frame and are spaced apart on the frame to contact the annular shape and provide a stable platform for the gauge system ; means for locating the gauge system relative to the annular shape and configured to axially and circumferentially position the gauge system on the annular shape , wherein the locating means comprises: locator pins mounted to the frame and extending in the outward direction from the frame and configured to locate the gauge system circumferentially using a circumferential locating feature on the annular shape , the locator pins and hanger pins extending in the outward direction from the frame and configured to locate the gauge system axially using an axial locating feature on the annular shape ; and at least one measuring means mounted to the frame , the measuring means comprising a housing secured to the frame , an anvil reciprocably received in a bore defined within the housing and biased in the outward direction relative to the frame , indicator means mounted to the anvil and biased therewith in the outward direction relative to the frame , and a probe of the indicator means biased in the outward direction relative to the indicator means to protrude from a bore defined in the anvil , the probe and the anvil being configured and adapted to provide a differential measurement of first and second surfaces of the interior surface of the annular shape . a frame ; means for securing the frame to an interior surface of an annular shape that has an axis and a circumferential direction, the securing means comprising multiple units that extend in an outward direction from the frame and are spaced apart on the frame to contact the annular shape and provide a stable platform for the gauge system ; means for locating the gauge system relative to the annular shape and configured to axially and circumferentially position the gauge system on the annular shape , wherein the locating means comprises: locator pins mounted to the frame and extending in the outward direction from the frame and configured to locate the gauge system circumferentially using a circumferential locating feature on the annular shape , the locator pins and hanger pins extending in the outward direction from the frame and configured to locate the gauge system axially using an axial locating feature on the annular shape ; and locator pins mounted to the frame and extending in the outward direction from the frame and configured to locate the gauge system circumferentially using a circumferential locating feature on the annular shape , the locator pins and hanger pins extending in the outward direction from the frame and configured to locate the gauge system axially using an axial locating feature on the annular shape ; and at least one measuring means mounted to the frame , the measuring means comprising a housing secured to the frame , an anvil reciprocably received in a bore defined within the housing and biased in the outward direction relative to the frame , indicator means mounted to the anvil and biased therewith in the outward direction relative to the frame , and a probe of the indicator means biased in the outward direction relative to the indicator means to protrude from a bore defined in the anvil , the probe and the anvil being configured and adapted to provide a differential measurement of first and second surfaces of the interior surface of the annular shape . <EOS>