In a book I produced with ConTeXt last year, I did a lot of calculation to be able to change the layout dynamicaly. With the actual version of ConTeXt I can't compile the book. I have tried a lot of things today ... without success. I hope my minimal-example helps you to understand, what I want to do - and what I am doing wrong: \starttext \setupexternalfigures[location={local,global,default}] \defineexpandable\ColumnA {30mm} \defineexpandable\ColumnB {40mm} \defineexpandable\ColumnABi {\dimexpr(\ColumnA + \ColumnB)} \defineexpandable\ColumnABii {\ctxlua{context(\ColumnA + \ColumnB)}} \newdimen\ColumnABiii \ColumnABiii = \dimexpr(\ColumnA + \ColumnB) A \ColumnA% ok B \ColumnB% ok % I sadly get only errors when I delete the comments: %ColumnABi: \ColumnABi %ColumnABii: \ColumnABii %ColumnABiii: \ColumnABiii %\externalfigure[cow][width=\ColumnABiii] ~ \page \stoptext