graph that illustrates the blanket normalized removal rate profile versus the retaining ring pressure referring to fig4 line s 1 0 signifies the initial pressure exerted by a retaining ring line s 5 signifies the pressure of line s 1 0 increased by 1 unit as can be seen the removal rate of line s 5 at the edge of the wafer is higher as compared to line s 1 0 line s 6 which signifies the pressure of line s 1 0 increased by 2 units has the highest removal rate at the edge of the wafer as can be seen the wafer edge profile is affected significantly by the changing retaining ring pressure as such as the retaining ring ages it is possible to compensate for the aging of the retaining ring by adjusting the pressure applied by the retaining ring fig5 a 5 b show a method for monitoring the groove depth of a retaining ring and adjusting the pressure applied to the retaining ring to compensate for the aging wearing out of a retaining ring referring to fig5 a one or more sensors 502 may be installed at a head cup load unload hclu to measure the groove depth of the retaining ring before loading a wafer the groove depth may be measured before each wafer or a batch of wafers being processed through standard cmp equipment which is depicted by p 1 p 2 and p 3 in fig5 a the batch of wafers may have 50 wafers in a batch or 100 wafers in a batch in other embodiments the batch may include other numbers of wafers in a batch in another embodiment the groove depth of the retaining ring may be measured after each wafer.