Stamps of PANAMA
Retardo Overprint  of 1910
This is a used example signed by Dr. Helme and Charlat.
This Mint retardo is a Genuine copy 1950 expertized by F.E.C. Friedl Expert Committee certificate # 2212B
Dr. Helme wrote: "Study of 3 covers, 2 genuine large multiples, several singles -- all known to be genuine; summary: counterfeit typewritten overprint  and counterfeit cancellations: (Excellent counterfeit -- The 9 of 1910 was the clue on the cancellation)"
Here is what I did, I took stamps #1 and #3 above and cut out the retardo and pasted it on stamp #2.  As you can see the 3rd "retardo" from the top shows a significant difference between the Genuine the letters between the "R" and the "e" they are separated, also the "e" and the "t" and the "o" are separated.  If you look at the genuine overprint the "o" is filled in.

This is a simple example of what a scanner can do.  Very accurate and fast identification.
Here are the detailed measurements of the "Retardo" Overprint of 1910 all measurements are in mm (millimeters) these  are at  +-0.2 mm of error.  Specially with this type written overprint.  The "Retardo" not always have the same width since typed letters would tent to move depending on the pressure given.  Another characteristic found would be that the letters with enclosure (R, e, a, d, o) have shades of ink inside of it.  Apparently Mr. R. D. Prescott was using a Densmore typewriter that had dirty letters.
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Letter
Width
Height
Top
Bottom
Top
Bottom
2.4
2.7
3.4
3.2
2.1
2.1
2.4
2.4
2.3
1.5
3.1
3.1
2.0
2.5
2.4
2.4
 
2.5
1.8
2.4
2.4
2.2
2.3
3.0
3.0
2.0
2.0
2.4
2.4
18.0
17.75
  Normal Position
 
17.5
17.5
Right Margin Position
Retardo
Retardo
e
t
a
r
d
o
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