You are confusing two things here. First the reason I said the step was 
too small is that is obviously wont work for 21 layers - but it will for 
say 5. This is why the 0.15 step is too small. Although simple it is crude 
 - which is why I advised not doing it! Either buy one or make your own by 
the method I described. 
Anyone who hasn't got a densitometer you can actually make them accurately 
enough by visual comparison with an existing step wedge if you can borrow 
one of these. It's not a bad idea to buy one and keep that in a safe place 
and make your own to actually use that match it.  If you are going to do 
any volume of work its handy to have quite a few isn't it. 
Second the writing on of the numbers is what you do on any step wedge that 
comes without them - either from Kodak or Agfa or one homemade by the 
simple method I described. Of course for the homemade one you do really 
need a few minutes with a densitometer to find the numbers, although it 
doesn't usually matter if they are accurate.
> 
> I would assume also (judging by my experience with the 19th-century 
> method
> of adding up pieces of translucent paper)  that numbers written on by 
> hand
> would get so strongly diffused through all those layers that the basic
> information of contact, sharpness and emulsion behavior conveyed by how 
> those numbers *print* would be lost.
> 
> Judy
> 
> 
Peter Marshall
On Fixing Shadows and elsewhere:
http://www.people.virginia.edu/~ds8s
Family Pictures, German Indications, London demonstrations & 
The Buildings of London etc: http://www.spelthorne.ac.uk/pm/