Despite the fact that PEST is freeware, it continues to be improved. Active research into model parameterization and predictive uncertainty analysis in the groundwater and surface water modeling contexts is ongoing - and many of the outcomes of this research will find their way into PEST and its supporting utility software. Yet PEST is more than just the most advanced package available for model calibration - PEST enables the quantification of model predictive error in a variety of settings. PEST is a move away from the paradigm of trial and error calibration and uncertainty analysis. No other package matches PEST's functionality, compatibility, performance, and extensive array of utility software.

Groundwater Vistas 5 is the only commercially available MODFLOW GUI that comes with PEST version 11. Additionally, Groundwater Vistas is the only GUI to offer the following features.

• Pilot Points & PEST: The pilot point calibration techniques in PEST are revolutionizing groundwater model calibration. GV5 will add many new ways of adding, editing, and optimizing pilot points.
• PEST & Regularization: GV5 supports two types of regularization. The original method from GV4 was preferred homogeneity ("smoothness") regularization. Preferred value regularization has been added to Version 5. In many cases preferred value regularization is more robust than preferred homogeneity.
• PEST & SVD: Singular Value Decomposition (SVD) is a new technique that allows estimation of many parameters with fewer simulations. The SVD-Assist process, however, is complex. GV5 simplifies SVD-Assist PEST runs-you simply follow a set of menu items in sequence to go through the SVD process.
• Improved PEST Error Checking: Pilot point runs with regularization and SVD are complex. GV5 now checks for all of the common errors encountered in these types of calibration runs.