I cant figure out this algorithm

[jcis]

I have a funtion drawing() like this:

private sub drawing()
max = calculate_max() 'determine max hight  
min=calculate_min()     'min height

 Me.ScaleHeight = (2.2 * (max - min))

me.refresh
vertical_coordinates <-----problem
draw things here.....
end sub

Eash time user puts a new terrain point (distance and height) in a Flexgrid and press ENTER this function is executed to resize and redraw.

Vertical Coordinates are the Y coordinates of the draw, that is
enclosed in a square i draw that is almost half the size of the screen. Look:

IMAGE LINK

Well, I cant show good coordinates where it says "here!"
I mean: there coord shoud be like 5 - 10 - 15 etc..
or 10-20-30. .etc
but with some numbers im getting somethig like:
21- 42- 63 (1 each 20).
OR: 547- 637- etc..
I need this coordinates to be rounded numbers like:
10, 15, 20... or 100, 200, 300.....or 540, 560, 580, etc

im trying something like:

dim hight as double
dim number as long

hight = max-min

do while max/10 <>int(max/10)  'is max divisible per 10
 max=max+1
loop

hight=max-min 'recalculate          
number=hight/10

do while min/10 <>int(min/10) 'is min divisible per 10
 min=min-1
loop

hight=max-min 'recalculate          
number=hight/10

now number has the distance between coordinates and I can
do something like this with each label:

Label1.Top = -min - number * 1 '  
Label1.Caption = Str(min + number * 1)
..... 
'(with each label)

'Here I use  -min to start   just
'in the bottom of the square, where the min is, and values are
'negative cause thats the way to go up in my form (incresing
'negative values

This is not working, im getting bad coordinates, like i said before.
Any idea about an algorithm to do this???

Thanks!
JCI