Process measurements made in chemical plants often do not satisfy material and energy balances due to random or possibly gross errors in the measuring device readings. Data reconciliation is a method of adjusting process measurements in a weighted least squares sense in order to satisfy the process constraints as well as minimise the difference between the process variable and the measurement of the process variable. Steady state simulation packages equipped with optimisation routines can be used effectively to perform data reconciliation and parameter estimation using existing built-in models which automatically satisfy mass and energy balance constraints. The time required to develop a data reconciliation problem can be significantly reduced by using these packages without sacrificing the quality of the results. Data reconciliation was performed on data from a pilot plant Agitated Thin Film Evaporator (ATFE) for concentrating sugar syrup using the AspenPlus simulation system. An AspenPlus simulation of the ATFE was developed using the built-in rigorous heat exchanger model, Heatx, and the rigorous two phase flash model, Flash2. The optimisation was carried out using the built-in SQP, (Sequential Quadratic Programme), optimisation routine. Data reconciliation improved the fit between the experimental data and the simulation model from between 30% and 98% as well as guaranteeing that the adjusted process measurements satisfy the mass and energy balances. The time required to develop the AspenPlus simulation and data reconciliation was about 1 h whereas a first principles simulation model developed using the programming language such as Fortran or C would take much longer to develop.