import math;
unitsize(1cm,1cm);

pen p(real a) {
    return linetype("0 " + string(a), offset=0, scale=false, adjust=false);
}
real a=.5mm;
add(grid(2,1,p(a)));

real a=1mm;
add(shift((3,0))*grid(2,1,p(a)));

real a=2mm;
add(shift((0,2))*grid(2,1,p(a)));

real a=5mm;
add(shift((3,2))*grid(2,1,p(a)));

shipout(bbox(.5cm,Fill(white)));