Bulova 1970 Accutron Calendar

I think this might be a Calendar O model of the 1971 Accutron but I'm not certain. The face and case are gold in color. The rear of the case indicates this is 14 KT gold filled. It has what I believe to be the original, leather band. This was given to my Grandfather as a 30 year work anniversary gift. There is documentation included with the watch to support that. This watch was handed down to me from my father. To the best of his recollection, this has not been worn since at least 1980.   The inside of the rear case cover has two numbers. One is 10-0 and the other appears to be 2661. There is also information regarding the battery stamped inside the rear case cover.   The movement is marked 2181.