Lovely Hamilton 992E railroad watch

Fine railroad watch made by Hamilton Watch Co. in 1939.
This is a Hamilton 992E, a development of the well proven 992 that features the innovative "Elinvar" hairspring and solid mono-metal balance wheel. A major problem with the carbon steel hairsprings that were commonly used up to this point was their timekeeping reliability when temperatures changed. A change in ambient temperature would alter the molecular make up of the spring and thus alter it's elasticity. A change of 1 degree could alter the timekeeping accuracy by as much as 10 seconds per day. To counter this, expensive to make Bi-Metallic split balance wheels were employed along with carefully matched balance timing screws. The "Elinvar" hairspring is an alloy and is resistant to changes in temperature, and as a bonus it was also found to be resistant to magnetism. 
So a mono-metal uncut balance wheel can be used which is much simpler to poise or balance. The effect of using the "Elinvar" spring and associated balance wheel was to provide much more reliable and accurate timekeeping throughout the temperature range.
The movement in this watch is mechanically and cosmetically sound. It features 21 jewels, a fully capped Swiss lever escapement with double roller, Sapphire pallets, gold timing screws and a sprung micro-regulator. Beautifully finished with a gold (alloy) centre wheel, gold jewel settings, and gilt inlaid script. The watch runs strong in all positions and keeps excellent time, it is crown wind and lever set.
10K gold filled "Bar over Crown" case by Wadsworth is in super condition. No dents or dings, no major abrasion beyond light scuff marks from age and use with all of the gold intact. Screw on / off front and rear covers with both doing so easily and both closing down square and tight.
Lovely double sunk, white enamel Montgomery dial in fine order with no flaws that I can detect.
A very good set of black enamelled spade style hands under a good mineral crystal.
 
Overall a fine example of this innovative railroader in beautiful condition and working as intended.