A dynamic alignment monitoring system allows an operator to monitor the misalignment of an on-vehicle disk brake lathe with respect to a vehicle axis about which the disk to be machined rotates, and can allow the operator to discontinue further alignment when appropriate in order to speed the overall time of the alignment process. The system processes signals from an angular rate sensor and a tachometer, using a scaling routine to derive a LRO value corresponding to the LRO of the disk which would result from machining in the current alignment condition. A representation of the derived LRO value is displayed to the operator. An operator override can allow the operator to discontinue further alignment adjustments when an acceptable alignment condition is indicated. The system can aid the operator by also presenting a representation of an acceptable LRO value for the particular vehicle being serviced.