I'm interested in change the natural numbering of one equation with \eqno{} but it does not follow the main font selected.
%%%%%%%%%%%%%%%%%%%%%%
\usemodule[simplefonts]
\setmainfont[Linux Biolinum O]
\setmathfont[Linux Biolinum O]
\starttext
I have the following expression
\placeformula
\startformula
y = Z \beta_1 + Y \beta_2 + u
\stopformula
that changes to
% \placeformula
\startformula
y = Z \beta_1 + Y \beta_2 + W_1\tau + u \eqno{ (1')}
\stopformula
\stoptext