Quote:
I have seen on another page a method to separate these stamps based on face value and I have not understood it.
Hi Roberto,
it is simple, (but your stamp covers it up)

With Sc#237 the designers name BERNH REBER is small
Sc#307 is larger (and by your stamp, the print screen has been enlarged slightly)
In the early Sc#237 the granite paper has different coloured lint variety.