Versatile twin-powered calculator with adding machine logic. Solar powered with battery backup prevents memory loss and keeps calculator running in all lighting conditions. Easy-to-read display with automatic three-digit punctuation. Auto power off after seven minutes. Power Sources: Battery Solar Display Notation: Numeric Number of Display Digits: 12 Memory: 4-Key/Secondary 2-Key. Green : Twin Power uses solar power except in low light conditions where battery power turns on. Also battery is mercury- and lead-free.