Shake this rechargeable calculator "briskly" left to right for 15-20 seconds and enough electricity is generated to operate the calculator for a few minutes. This is a great interactive, technological promotional product for your message. When the LCD display dims, simply shake again to recharge - calculations will not be lost during recharging. Available in black, purple, green, and red with metallic silver trim, ergonomic rubber keys, and clear acrylic chamber to show Faraday's electromagnetic charging. Never need batteries. Individually gift boxed.