Unisonic always was a good bet when it came to calculators for school and work. I would buy them at my local K-Mart store. Of all the Unisonic calculators and there were many, I always liked the small 940. I had a 940 with me all during my career in the military.Top row are the 940s. First one is a 940, than a 940 A and a 940B. Variations are in the key layout. All three have green LED numbers. Bottom row are the 911, 911L and the 931. The 911 has green LED display and the 911L has a red display. The 931 also has a green LED display. 911 and the 931 have the square root key. These are all great calculators from the 70s. They were made in both Japan and Taiwan. Add them all to your collection.