 It replaced the QT-8D's integrated power supply with a rechargeable battery pack, but it was otherwise nearly identical to the QT-8D.The four ICs of the QT-8D and QT-8B were also used as the basis of the Sharp EL-8, one of the first mass-produced hand-held electronic calculators, introduced in 1971.Sharp also built OEM versions of the QT-8D for the Swedish office machine company Facit and its subsidiary Addo, which sold them as the Facit 1115 and the Addo-X 9354.