[Milsurplus] Parts ID

[Lloyd KK7IZ]

I just received 2 units, identical except 1 has no ID tag. Tag on 1 unit 
reads:
Signal Corps
Wireless Sets No19 MK ll
Aerial Variometer
Z.A 10214    P.C. 75608C
(Serial No 10xxx)  CZR 12440-Phila-44

Approx 5" dia x 9" long cylinder, knob and scale (visible thru small window) 
on 1 end, connectors, 1 on side, 1 on end oposite knob.
Ive seen a lot of stuff but this is a new one on me.
Rarity and value?
Thanx
Lloyd  KK7IZ
kk7iz at cox.net

Lloyd Godsey  KK7IZ
1315 N. udall Circle
Mesa, Az  85203
480-620-7145 (cell)
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