CONST 
  Gap = 2, 
  Num = 60, 
  Total = Gap * Num + 1;

PROC DrawLines(a, i, xK, yK) IS 
  VAR x, y IN 
    x := i * Gap * xK; 
    y := Total * yK; 
    PS.MoveTo(R2.Plus(a, (x, 0))); 
    PS.LineTo(R2.Plus(a, (x, y))); 
    x := Total * xK; 
    y := i * Gap * yK; 
    PS.MoveTo(R2.Plus(a, (0, y))); 
    PS.LineTo(R2.Plus(a, (x, y))); 
    PS.Stroke() 
  END 
END;

PROC Grid(a) IS 
  VAR x, y, i = 0 IN 
    x, y := Unit.Pixel(); 
    PS.SetWidth(0); 
    DO 
      i <= Num -> 
        DrawLines(a, i, x, y); 
        i := i + 1 
    OD 
  END 
END;

UI PointTool(Grid);

PROC Square(a, sz, label) IS 
  VAR b IN 
    b := R2.Plus(a, (sz, sz)); 
    Rect.Draw(a, b); 
    PS.Stroke(); 
    TypeLinesC.Center(Geometry.Mid(a, 
                                   b), 
                      label) 
  END 
END;

PROC Cmd0() IS 
  IF 
    VAR 
      a ~ (51.31, 50.62), 
      b ~ (175.2, 48.52), 
      c ~ (48.38, 155.4), 
      d ~ (160.5, 138.5) 
    IN 
      Grid(a); 
      Square(b, Unit.In * 1, "1 in"); 
      Square(c, Unit.Cm * 3, "3 cm"); 
      Square(d, Unit.Mm * 40, 
             "40 mm") 
    END 
  FI 
END;