awk '
BEGIN {
pos='$1'
}
{
ligne[NR]=$0 
}
END {
nr=NR/2
l=1
for (i=1;i<=nr;i++) {
n=substr(ligne[l],pos,5) +0
k=l+1
m=substr(ligne[k],pos,5) +0
dif =n-m
diff += dif
difg += (dif * dif)
l=l+2
}
moy=diff/nr
ect=sqrt((difg - diff * diff / nr) / (nr-1))
printf "\n Difference moyenne = %7.3f\n",moy
printf "\n Ecart type         = %7.3f\n\n",ect
} '