MACSEstimator is an online property estimation and sensor validation application, also known as a "soft sensor". Using advanced statistical modeling techniques, MACSEstimator can use easy to measure continuous process variables (such as temperature and pressure) in order to estimate more difficult or less frequently measured parameters such as a stream quality. A member of the MACS^TM family of advanced control products, it is easily configured, and provides a rich set of data validation tools and high frequency quality estimates necessary for closed loop advanced control. Model accuracy is sustained by on-line model updating with periodic laboratory or on-line analyzer feedback information. MACSEstimator can be integrated into an online advanced control application MACSRuntime, or is available as a standalone module for Operation’s use.