Fritz Jooste Administrator Posts: 6 7/12/2016

Fritz Jooste Administrator Posts: 6 The Rubicon Online Deflection Analysis tools use the following approach to calculate errors during backcalculation: Step 1: Calculate the absolute difference between the Measured and Calculated deflection (= A) Step 2: (a) If the difference is less than the Precision level X, then the error at that sensor is regarded as zero; (b) If the difference is more than the Precision level X, then reduce the difference by subtracting the precision, to get B = A - X; Step 3: Calculate the percentage error as: Error = [B/(Meas + 0.001)] * 100 % Note that: The precision level X is now set to 5 micron. In the older Rubicon Desktop procedure a slightly different algorithm was used with a 10 micron precision. Explanation: The reason for the precision correction is to ensure that small deflections, such as those often measured at the outer sensors, do not distort the apparent percentage error and inappropriately drive the backcalculation process. For example, if the measured outer sensor deflection is 4 micron, and the calculated outer sensor deflection is 8 micron, that would register as 100% error even though the absolute difference between measured and calculated deflections is less than 5 micron. By making a correction to take into account the precision of measurements and slight instabilities at the surface, a more reasonable error is calculated, thus ensuring that the backcalculation algorithm focuses on the "big picture", much like an experienced analyst would do in a manual backcalculation. Note that the 0.001 adjustment in the final step 3 above is done to ensure stability when measured deflections are zero or very close to zero. By adding 0.001 to the Measured deflection, a division by zero error is always avoided.

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