JavaScript must be enabled in order to use this site.Please enable JavaScript in your browser and refresh the page. GLM, GLZ, GRM, PLS, and GDA Syntax - Keyword Surface SURFACE [=] Continuous predictor (covariates) list; Example SURFACE = TIME DEGREES;Optional keyword, currently not used in computations; specify the continuous predictors (covariates, specified via the COVARIATE keyword) that are used in a response surface design (as specified via the DESIGN keyword). Applies to GLM, GLZ, GRM, PLS, and GDA. Copyright © 2021. Cloud Software Group, Inc. All Rights Reserved.