Quantifying uncertainty can be a very useful and often important aspect of evaluating results of calculations, particularly in modelling. The same applies for spatial layer mashups where the grids provide the input variables for equations that are calculated spatially (i.e. raster calculator). This toolbox for ArcGIS uses standard error propagation equations to simultaneously calculate the result of basic math expressions along with the estimated error of that result. The measured or estimated errors for the input variables are required. Error covariances can also be included in the calculation of error propagation, but are not required.