[QUOTE=Versuch;2072994]I have been told that this is a boost gauge…….I am not so sure .
Over to the experts.

I think it is. It’s from the late 20’s. I have seen similar boost gauges before with the plus and minus words printed on the dial in this style, but with a different pressure range.

AERO URINARY APPARATUS, MARK I

I have an Air Board specification from May 1918, for the, AERO URINARY APPARATUS, MARK I.

The device has the following general description:

General Description.—The apparatus consists of a rubber funnel attached at its smaller (and lower) end to a length of rubber tube, terminating in an elliptic container. Attached to the top of the funnel is an internal conical sleeve of soft rubber, the annular space between funnel and sleeve forming a trap preventing any back-flow from the connecting tube. A non-return valve of the rubber flap type is provided in the upper end of the container and a screwed vulcanite or ebonite drain plug in the lower end, the cap of the drain plug being retained by a short chain. Two rubber lugs attached to the funnel are adapted to button to an adjustable waistbelt, which supports the apparatus in use, and a suspensory bandage is attached to the lugs and to the belt by tapes. An adjustable elastic strap keeps the container against the leg of the wearer.

AAP318 (Standard notes for wireless maintenance mechanics and wireless assistants) gives the following information:

1. Cables.—(i) Core.—The number of cores in a cable is indicated by the prefix to the class name :—

Uni means one. Quinto means five.
Du means two. Sexto means six.
Tri means three. Septo means seven.
Quadra means four. Nono means nine.

(ii) Covering.—The nature of the covering is usually indicated by the main part of the class name :—

(а) Flex . . Coloured cotton braiding.
(b) Proof . . Cotton braiding, waterproofed by varnish.
(c) Sheath . . Tough rubber sheath.
(d) Core . . Tough vulcanised rubber, coloured red.
(e) Cel . . Cotton braiding, waterproofed by coloured cellulose.
(f) Met . . Lapped with varnished cambric, and braided with metal wire.
(g) Com . . Metal braided, compounded with rubber.
(h) Lead . . Lead covered.

(iii) Rating.—The number following the cable name indicates the normal (maximum) current rating of each core in amperes, thus “uniflex 4” will carry 4 amps., and “dusheath 19 ” will carry 19 amps.

With the normal current flowing, the volts drop per yard is 0.1 volts for the smaller cables (4, 7, 19), and less than this for the larger.

Dimensions may help.

This site offers a description with dimensions

http://daryl.chin.gc.ca:8001/SEARCH/BASIS/humqa/user/object/DDW?W%3Dinsfull++%3D+%27CANADIAN+WARPLANE+HERITAGE+MUSEUM%27%26M%3D16%26K%3DACSJ004.126.001%26R%3DY%26U%3D1

P & P
There is another RAF instrument manual issued that dates before the AP1275. It was issued in 1921. It does not have Section Reference numbers as it predates that system. It uses Mark numbers when referring to instruments.

Send me a picture of the altimeter in question and I will attempt to identify.

The Mk V is calibrated to 16000ft and seems to have been made by both Short & Mason and T. Wheeler.
The Mk VA appears to have been made by both Short & Mason and Zenith and is calibrated to 20000ft.
The Mk VB is a Smiths Model AV.563 calibrated to 28000ft. According to the specification the dimensions are shown on drawing A.B. T. 8/92.
My data shows that the case is 4 7/16″ in diameter. The case size for the Smiths AV.572 is 3 7/8″.

According to A.P.1275B, Vol. I, Sect. III, Chap. 2 (A.L. No.33 January, 1945), it has this to say about the P.8 and P.8M compasses:

17. The P.8 compass is similar to the P.4 compass except that it is modified in certain details of its construction, moulded plastic parts being substituted for metal wherever possible. The bowl is made of metal on account of the incorporation of a bellows, but the floating ring and the grid ring are of moulded plastic. P.8M differs inasmuch as it has increased magnetic moment and E-W parallel steering. The three compasses P.8, P.8M and P.11 have the same purpose and function, and the provision for fitting them to aircraft is the same.