Displaying readings on an analog scale, where the digital characters are printed on the scale in the different locations that the pointer swings is not an issue. But, putting digits on a digital readout where different digits must share the same location, is more difficult. Three ways have been used: the solid character, the dot matrix, and the bar segments. The solid character can be the most pleasing way of displaying digits, but it is problematic since they must all share the same space. This was the way the servo wheels worked, and electrically, it was done with Nixie tubes. These used ten transparent in-line wafers enclosed in neon gas. Each wafer had electrodes in the shape of numerals, which glowed when the wafer was electrified. Although the unused wafers were still discernible while one wafer glowed, it was tolerable. The Nixie tube was used for years and can still be found on special equipment. However, this method is costly and the tubes are fragile.