And excellent perf gauge measurer can be found here http://itunes.apple.com/us/app/stamp-analyser/id525729462?ls=1&mt=12
All thanks to http://rakim.com
The Perforation Gauge was invented by Dr Jacques Amable Legrand of Paris in 1866. This simple device, measuring the number of holes in a line two centimetres long, is universally used to this day.
Perforation definitions follow the French convention of measuring the average distance, in millimetres, between the centre of each hole on a stamp along each axis. Since the distance between each pair of holes could vary quite considerably due to bending pins of the perforator, and the width of the hole, the overall average distance across an axis is used.
As a side note, for many years, Australian printers were advised to perforate their stamps at '16 holes to the inch' (approximately perf 11). A clever definition which involved the continuous, and easy halving of an inch of perforator to insert the pins.
Measurements are defined from the bottom axis of the stamp, rotating clockwise. Thus, for an imaginary triangular issue (never done in Australia) the specification would be perf 11 x 12 x 13. An imaginary, standard rectangular stamp is defined as 11 x 12 x 13 x 14.
Where opposite sides of a stamp are not the same perforation, they are declared 'mixed perf' (as in this imaginary example). Australia never issued mixed perf stamps (Australian Colonies did).
An imaginary stamp of perf 11 x 12 x 11 x 12 has equal perforations on each side. In this example the bottom and top are perf 11, the sides are perf 12. By convention, these stamps are conveniently abbreviated to perf 11 x 12.
Similarly, a stamp which has equal (or almost equal) perforations on all sides is simply, and conveniently, defined as perf 11 rather than perf 11 x 11 x 11 x 11.
Exact Perf measurement.
Perforation measurement is an inexact science, it is not meant to be, nor was it ever intended to be, a scientific response. Identical perforators were used across many issues and for many years (obviously with corresponding maintenance and fresh pins). This same perforator could be defined differently relative to the stamp according to circumstance. Always with the intention in mind of alerting the philatelist to subtle differences of the stamp issue on hand, not the perforator.
Unless there is some fine discrepancy between identical issues on different perforators. Perf definitions are always approximate and taken to the closest millimetre. A stamp measuring 11.3 for example is generally referred to as a perf 11 stamp, simply because the finer measurement is not relevant and probably wrong anyway.
By convention, finer measurements are defined in quarter units, only when necessary. These circumstances arise when
The reader is warned, not to treat perf specifications as absolute measurements, they are indications of the difference between varieties only, sufficient enough solely to distinguish these differences, but not to examine an issue under a microscope which is unnecessary.
Comb versus Line Perforation.
Identical stamps with identical perf measurements differed by being perforated with a line or a comb perforator.
Originally all stamps were line perforated. A device which acted almost identically to a guillotine in that a single row between stamps were perforated, stepped, perforated, then the sheet turned 90 degrees and the process continued. Naturally, these stamps are almost always a single perf such as perf 11 all around.
Missing perfs and severely misplaced perforations are quite common on early issues for this reason.
During the introduction of the KGV series circa 1915 a comb perforator was purchased and its operation eventually took over completely. The roll of the comb was sized to have the same circumference as the stamp. Thus in any one rotation, three sides of a stamp were perforated. As the comb continued to be rolled across the sheet, the next progressive rows of stamps were perforated. A huge saving in time.
The nature of rolling a comb across a print-sheet means that at least one side-margin of a PO sheet is always perforated through as the comb runs off the edge of the paper.. Which side(s) depend on the orientation of the image (portrait or landscape). The margin(s) so affected are always left and right OR top and bottom (but not both). It is impossible to find sheets perforated in the opposite orientation for that issue (top and bottom vs left/right) as the comb roller was not sized in circumference to do so.
The zoological definitives are an example. The 640 on Landscape denominations can only have top / bottom perforations, The 640 on portraits can only be left and right.
Since all coil-sheets zoologicals are portrait, they are always perforated across the sheet, the Robes, derived from the original Victorian Centenary layout were perforated UP the sheet.
Because the post office sheets were always a sub multiple of the printsheet (often up to 6), and because the comb was applied to the printsheet, not the post office sheet, sheets issued to the post office can be found perforated right, left or both margins respectively (for portrait issues).
There is one important difference between line perforated and comb perforated issues that make them separately collectible. It was virtually certain that on a line perforated stamp, the corners of that stamp would not line up perfectly to two separate punches by the perforator. Whereas, on comb perforations, there is always a neatly defined hole in each corner of the stamp.
Portrait versus Landscape orientation.
As stated, Australia has only ever issued rectangular stamps (including the square-sided arms series), and their perf definition is always from the bottom of the stamp. This relative measurement is in respect to the visual image of the stamp.
This sometimes does not correspond well to the printsheet layout of those stamps. This work concentrates heavily on the printsheet, the imprints and layout (on the electroplates) of the stamp issues. As such some discrepancies must creep in when defining some very few issues in this handbook versus a standard catalogue.
A classic example of the difference is in the zoological series. The greatest majority of all these stamps were in portrait orientation. Only two, the 9d platypus, and the 5d ram, were in landscape orientation. From the printers perspective, it made absolutely no difference. They were laid out, printed, and perforated as portrait issues. Their dimensions and definitions are described from the printers perspective and as such reflect portrait perforations, and portrait plate layout, the direct opposite of a catalogue definition.
This author recommends however, that the collector stick with convention in collecting issues, while retaining an understanding of why this handbook needs to be slightly different.
For a further discussion and better understanding of this perforation issue see the zoologicals.