Thanks to an impassioned entreaty from Natalie (of the CTDA, I am guessing), I managed to track down the elusive source of the Perkins Tailoring Devices.
These, however, only measure the slope of the shoulder. The full; kit of Perkins devices also include in incline device to measure the prominence of the shoulder blades, a rise device to measure for trouser rise, a sleeve device to measure from the pit of the arm to the wrist or the tip of the thumb, a device known as a trouser length/low shoulder device which is intended to also capture the estimated 15-20% of people whose shoulder is low at the collar edge and not merely at the shoulder point.
I haven’t used most of the devices so I can’t say much about them other than that they could make standardization simpler, particularly where stores are communicating measurements to factories for MTM programs.
These can be purchased at perkinsdevices.com