DUAL POWERSolar (works only when it is bright) and Battery (one AA battery NOT included). If the solar panel receives insufficient light, the numbers in the display will disappear. Please insert one AA battery for continuous and accurate usage. BIG BUTTON DESIGNLarge non-stick plastic button, new material, more durable. The calculators adopt scientific big button design in line with the use of human habits and comfortable for touch. 12 DIGITS CALCULATOR12 digits easy to read and make the calculator most useful for large calculations. Specially modulated pigment for the display screen which improves the clarity of the display screen clearly. LARGE DISPLAYLarge eye-angled, upright display, erginiomic angle design for best user experience. Easy to read, easy to carry. GREAT VALUE OF 2 PACKSplaks basic office calculators perfects for office, business, school calculators for students, store, mall daily and office home used. Auto-off when you do not use it about 10 minutes.