I would like create six or more ammeter with different readings, but i'm not able to do that because metapost create the same random number every time I call the buffer that defines my ammeter.
My code:
\startbuffer[ammeter]
\startMPcode
r := 4cm; len := 10bp; min_thickness := 1.75bp; hour_thickness := 3bp;
path cadran; cadran = fullcircle scaled (2r);
numeric escala;
escala := 0;
for i = 50 upto 70:
if i mod 5 = 0:
j := i div 5; angl := 90-30j;
freelabel("\tfb\bf" & decimal escala, (r+len)*dir angl, r*dir angl);
draw ((r, 0) -- (r - len, 0)) rotated angl withpen pencircle scaled min_thickness;
escala:= escala + 0.5;
else:
angl := 90 - 6i;
draw ((r, 0) -- (r - .5len, 0)) rotated angl;
fi
endfor
pickup pencircle scaled min_thickness;
numeric minute;
%randomseed := uniformdeviate infinity;
minute:= 50 + uniformdeviate(20);
pair A, B, C;
A:=1.6r*right+.5r*up;
C:=1.6r*right+.8r*up;
B:=1.1r*left;
drawarrow origin -- r*dir(90-minute*6) cutends (0, 1.5len);
fill fullcircle scaled .75len;
draw unitsquare xscaled 3.2r yscaled 1.5r shifted B;
label("\tfb I (A)", 1.2r*up+1.6r*right) withcolor red;
draw fullcircle scaled 2len shifted A;
draw fullcircle scaled 2len shifted C;
\stopMPcode
\stopbuffer
\startbuffer[programa]
\placefigure[center,nonumber]{}{
\startcombination[2*1]
{\externalfigure[ammeter][type=buffer,width=8cm]}{\_\_\_\_\_\_\_\_\_\_$\pm$\_\_\_\_\_\_\_\_}
{\externalfigure[ammeter][type=buffer,width=8cm]}{\_\_\_\_\_\_\_\_\_\_$\pm$\_\_\_\_\_\_\_\_}
}
\stopcombination
\stopbuffer
\starttext
\dorecurse{3} {\getbuffer[programa]}
\stoptext