This probably was built at the Indiana Band Inst. Co. after they were bought by Martin in 1928. It has the aux Eb on the front rather than the rear which is much better as it is a direct action. Probably does not have the high C# adjuster which may make C#3 and D3 sharp. Basically similar to a HC series 2 with that key modification on Eb. I have the same horn marked Indiana and it was made in 1933 and I would put yours in that area.