In some cases, burst tones were used to select repeaters. By changing tones, the mobile radio would actuate a different repeater site. A typical tone scheme might use the tones 1,800 Hz, 2,000 Hz, 2,200 Hz, 2,400 Hz, and 2,552 Hz. This was the scheme used by most State of California agencies during the era when tone burst was in use. Some systems have been observed to use tones as low as 800 Hz. The default or standard five Motorola tones used for single tone format as of the 1980s: 1,350 Hz, 1,500 Hz, 1,650 Hz, 1,800 Hz, 1,950 Hz. These were identified in system documentation for a number of remote control equipment models as well as sales brochures for Motorola Syntor and Micor mobile radio "Systems 90" accessories. A common tone burst frequency used by many amateur radio systems in Europe is 1,750 Hz.