This aluminum needle-based electroscope’s design makes it superior to traditional leaf-style electroscopes in part because the needle stays put when experiments are being performed, versus 'old' electroscopes where the leaves ‘flutter.' The ultra-sensitive needle pivots on an axle when an electric charge is applied to the disk located at the top of the electroscope. 2.4 x 3.7 x 4.1 in. (60 x 95 x 105mm). Ring diameter 150mm.