How much can the mixed standard ?Ct values vary in the KRAS PCR kit?

The mixed standard ΔCt values may vary in the KRAS PCR kit.  Some variation is expected between runs and on different machines due to changes in threshold settings. Approximately ±2 Ct from the values given in the instructions is acceptable variation. If the variation exceeds this, check that the kit is within the expiry date. Another possible source of variation is the real-time PCR machine running hot or cold. It is recommended that all machines to be used with the kit be calibrated at regular intervals as suggested by the manufacturer.