Hi, Here is my test: =================================================== \setuppapersize[A4][A4] \usetypescript[postscript] \setupbodyfont[palatino,12pt] \starttext \startformula K = \frac{\sigma_1}{\sigma_2} = \frac{355}{14}= \ctxlua{tex.print(355/14)} \stopformula \stoptext =================================================== It works well and give me result = 25,357142857143. In order to obtain 2 decimal number I tried: \startformula K = \frac{\sigma_1}{\sigma_2} = \frac{355}{14}= \ctxlua{tex.printf("%0.2f",355/14)} \stopformula But it does not work. Here is the error: tex.printf("\doplaceformulanumber \stopdisplaymath \global \let \gdef \ETC. ! File ended while scanning text of \zerocount. <inserted text> } <*> ./test-lua.tex ? Another try: \startformula K = \frac{\sigma_1}{\sigma_2} = \frac{355}{14}= \ctxlua{tex.print(string.format("%0.2f",355/14))} \stopformula gives me the same error. So is there really a function printf() in LuaTeX engine ? Thanks