This knowledge base article discusses how to use FRED’s Pre-Update Script tool to implement pickup parameters, similar to what you might find in a sequential lens design code. A pickup parameter is traditionally used to tie one surface parameter to another, setting RB = -RA, where RN is a surface’s radius of curvature. The use of Pre-Update Scripts expands upon the traditional options available as pickups, since virtually any parameter in the model is accessible through FRED’s scripting language. More generally, pre-update scripts can be useful for controlling system configurations through the use of global script variables. This both eliminates the need for unnecessarily editing the model by hand in multiple places as well as reduces the risk of human error.