# Permissible calculation tolerance with forward / backward transformation (P-CHAN-00228)

P-CHAN-00228 | Permissible calculation tolerance with forward / backward transformation
Description | Especially when self-created kinematic transformations are used (see [McCOM-TRAFO]), this parameter can maintain the required position consistency in the NC channel. The result of the calculation sequence (Input values - Forward transformation - Backward transformation - Output values) must match the input values within specific limits.

Therefore, the CNC checks whether these deviations are within the permissible tolerance according to the parameter and generates an error message if necessary. The default tolerance value here is 0.3 µm.

Due to internal algorithms (e.g. iterative solution method, numeric inaccuracies), this may lead to greater deviations which then require adjustment using this parameter.

Parameter | permitted_trafo_deviation_limit
Data type | UNS32
Data range | 0 < permitted_trafo_deviation_limit < MAX(UNS32)
Dimension | 0.1µm or 0.0001°
Default value | 3
Remarks | Setting large tolerances should be avoided since this may cause relatively large position jumps which can lead to the response of the dynamic monitoring function. The standard tolerance value here should be maximum 0.5 microns. Therefore, when self-created kinematic transformations are used, the internal algorithms must first be checked before setting excessive tolerance values.