An apparatus, system, and method are disclosed for calibrating an estimate of the status of a mechanism or process, for example, particulate production from a diesel engine. A first estimator makes a first particulate production rate estimate as a function of, for example, differential pressure over a particulate filter over time, a second estimator makes a second particulate production rate estimate by interpolating between high and low production rates, and a calibrator calibrates the second estimator according to the difference between the first and second estimates. The calibration may be carried out by calculating new high and/or low production rates, and may depend on the reliability of the first estimate.