[NTG-context] Scale content to height of the font, measure font height

Hi, I'd like to scale something (actually a symbol drawn in TikZ) to the exact high of the char 'M'. I found the scale environment for it but struggle to measure the correct font height. I found the "definemeasure/measure/measured" commands but they define a dimension and are not for doing measurements on rendered text. Is there a simple way to get the height a char as a dimension? MWE: ``` \starttext % Is it possible to replace 1cm with a common expression? This is the letter M. \scale[height=1cm]{a} should have the exact same size as M. This should also be true {\tfc with a bigger M. \scale[height=1cm]{a}}. \stoptext ``` Best Gerion