graphics 400,600
gcls
a = 399 'Bug - a can't go to 400 - goes into never never land if a = 400
for x=0 to a step 10 '
line x, 0, x, 600, 0
next x
b = 589 'Bug - b can't go over 589 - goes into never never land if b = 590 and more
for y=0 to b step 10
line 0, y, 400, y, 0
next y
end