From the USHMM:
"Originally, a special metal stamp, holding interchangeable numbers made up of needles approximately one centimeter long was used. This allowed the whole serial number to be punched at one blow onto the prisoner's left upper chest. Ink was then rubbed into the bleeding wound."
The above description is at odds with that in the Telegraph article.
"When the metal stamp method proved impractical, a single-needle device was introduced, which pierced the outlines of the serial-number digits onto the skin. The site of the tattoo was changed to the outer side of the left forearm. However, prisoners from several transports in 1943 had their numbers tattooed on the inner side of their left upper forearms. Tattooing was generally performed during registration when each prisoner was assigned a camp serial number. Since prisoners sent directly to the gas chambers were never issued numbers, they were never tattooed."
From the above it would appear that the individual number metal stamps were dropped in favour of a single needle device.
I presume the Auschwitz museum will have set the metal stamps that they have into a line of numbers that can be compared to the numeral spacing on a survivors tattooed arm?
An interesting find if they are what they purport to be...I am slightly sceptical.