Here's a way to tell one from another!
First of all, neither perforation gauge not watermark detector will help. All the issues are perf 11 x 12, and all are watermarked Crown and GvR (Scott wmk #34). So where to start?
The easiest path is to start with the latest issue and work backwards.
The last issue (Scott #222-24) is the easiest to tell. It is called the "Waterlow re-engraved issue". Look at this picture:
The Waterlow re-engraved issue of 1934 (Scott 222-4) has a cross-hatched background behind the king's head. All the others have only horizontal lines. If your's is cross hatched, you've identified it! If it has horizontal lines, more investigation is necessary.
Ok, so you have horizontal lines -- could still be one of three issues. Look at this picture.
See the dot in the top center of the stamp in back? If your stamp has one, you have identified it. Only the Bradbury Wilkinson (BW) printing of 1919 has the dot (Scott #179-181). If the dot is there, it's definite, but not all the BW stamps have the dot! so the absence of the dot proves nothing!
No dot? Check the vertical dimension, from outer frame-line to outer frame line. The BW stamps are 22 3/4mm. If that's yours, you have Scott #179-81 -- dot or no dot! The remaining two possibilities are only 22mm. The difference doesn't sound like much, but if you have a good perf gauge, it should have a precise millimeter scale, and the difference is obvious. These pictures are not to scale!!
So your stamp is 22mm high! (It had better be at this point, or you missed something!) Still two choices -- the two earliest printings. Scott #173-176 was printed by Waterlow Brothers & Layton Printing in 1913. Scott #173a-75a was printed by De La Rue & Co.
Look at this picture:
Now you look at the perfs. De La Rue (#173a-75a) has two big teeth top right and top left, plus smaller perf holes. This is the trickiest step and a reference copy would help a lot. But look at a few and you will soon see the difference.
Now go to your local stamp club and be the expert!