I am using \externalfigure to show a picture at the desired scale. Instead of providing a number for the width parameter I have made a definition with \def. When I run in mkiv this I get the text "4t" alongside the picture.

 

\def\DesignSize#1{3.5cm/4*#1}%

\starttext

\externalfigure[hacker.jpg][width=\DesignSize{4}]

\stoptext

 

In mkii is perfect.

 

I've also tried

 

\define[1]\DesignSize{3.5cm/4*#1}

 

with the same result.