Hello,
I discovered ConTeXt gradually, so be indulgent please.
With the following command :

[parabole1.pdf][scale=0.8]

I have the following error message :

! Missing = inserted for \ifnum.

system          > tex > error on line 1 in file /home/fab/demo1.tex: Missing = inserted for ...

1 >> \setuppapersize[A4]
2     \setuplayout [backspace=0cm,width=middle,
3     topspace=1cm,height=middle,
4     location=middle,marking=on]
5     \setuppagenumbering[location=]
6     \loadtypescriptfile[mathdesign]
7     \setupbodyfont[charter]
8     \setupexternalfigures[location={local,global,default}]
9     \setupTABLE[r][1,2][height=1.5cm,width=9cm,align={middle,lohi}]
10     \setupTABLE[r][3][height=6cm,width=9cm,align={middle,lohi}]
11     \starttext

<to be read again>
.
\p_scale .-0.
             8
<argument> ...ale \empty \plusthousand \else \ifnum \p_scale
                                                  =\zerocount \plusthousand ...
\luaexpr #1s-\directlua {tex.print(tostring(#1
                                              ))}
\grph_scale_apply_scale ... \else #2\fi \fi /1000}
                                                  }
\grph_scale_by_scale ...le_used_x_scale \p_xscale
                                                  \grph_scale_apply_scale \m...
...
l.17 \eTABLE
          }
?
! Emergency stop.

system          > tex > error on line 1 in file /home/fab/demo1.tex: Emergency stop ...

1 >> \setuppapersize[A4]
2     \setuplayout [backspace=0cm,width=middle,
3     topspace=1cm,height=middle,
4     location=middle,marking=on]
5     \setuppagenumbering[location=]
6     \loadtypescriptfile[mathdesign]
7     \setupbodyfont[charter]
8     \setupexternalfigures[location={local,global,default}]
9     \setupTABLE[r][1,2][height=1.5cm,width=9cm,align={middle,lohi}]
10     \setupTABLE[r][3][height=6cm,width=9cm,align={middle,lohi}]
11     \starttext

<to be read again>
.
\p_scale .-0.
             8
<argument> ...ale \empty \plusthousand \else \ifnum \p_scale
                                                  =\zerocount \plusthousand ...
\luaexpr #1s-\directlua {tex.print(tostring(#1
                                              ))}
\grph_scale_apply_scale ... \else #2\fi \fi /1000}
                                                  }
\grph_scale_by_scale ...le_used_x_scale \p_xscale
                                                  \grph_scale_apply_scale \m...
...
l.17 \eTABLE
          }
! ==> Fatal error occurred, no output PDF file produced!
mtx-context     | fatal error: return code: 1

This comes from the option scale = 0.8, because without it, the code compiles without problem.
Thank you.