Dear List, 

i have the little following example: 

\setuppapersize[A8,landscape]

\setuplayout[leftmargin=2.5cm,

             leftmargindistance=0.2cm,

             backspace=2.9cm,

             width=4cm]

\showframe

\starttext

\blackrule

\margintext{Me}

\blackrule[color=black, height=0.5ex, width=1cm]

\stoptext

\startformula

a^n + b^n = c^n.

\stopformula

\stoptext