You found yourself a gold nugget! According to this site, it's 1926-27.
http://indiangauge.com/ORIGINAL%20AMP%20GAUGES%20FOR%20SALE.html
Although that one doesn't have some of the writing that yours has at the bottom of the face, so more research might be in order.
I think it's safe to say it's late-'20s to 'early-'30s and will sell for several hundred dollars.
Put that sucker on eBay Motors for a $9.99 opening bid and no reserve and sit back and watch the fun!
Put it in Parts & Accessories>Motorcycle Parts>Antique.Vintage,Historic and maybe a second category of Collectibles>Transportation>Motorcycles>American>Indian
Be sure to spell motorcycle at least once without the 'r', as that's the way Indian did it - Indian Motocycles. Good luck!