[NTG-context] read out of \tx-value possible?

Hi folks, is it possible to read out the value of \tx (or \txx ... )  for calculations if bodyfont and fontsize is given? \the\tx doesn't work.     \setuplayout[grid=yes]     \setupbodyfont[libertinus,12pt]     \setupinterlinespace[1.25\bodyfontsize]     \starttext     \samplefile{tufte}\par     \startlinecorrection     \setuplocalinterlinespace[12.5pt]     \placefigure [middle,nonumber]{\tx\midaligned{bla blablabla blabla\\ blubdibla blabla bla}}             {\externalfigure[][height=40mm, width=60mm]}     \stoplinecorrection     \samplefile{tufte}\par     \stoptext I would like to calculate the setuplocalinterlinespace similar to the setupinterlinespace. Thanks in advance Thomas