Oscilloscopes with two vertical inputs, referred to as dual-trace oscilloscopes, are extremely useful and commonplace. High impedance inputs are preferred on measuring instruments such as voltmeters or oscilloscopes. They are available for both voltmeters and oscilloscopes. Tektronix vintage analog oscilloscopes technologies and evolution. Tektronix was heavily involved with designing digital sampling oscilloscopes. More sophisticated analog oscilloscopes contain a second timebase for a delayed sweep. Current probes can be used both by measuring instruments and oscilloscopes. RCA Made equipment for repairing radios such as oscilloscopes. In the mid-1980s, they quickly replaced their analog oscilloscopes. These are found in "analog phosphor storage oscilloscopes". Some analogue oscilloscopes feature a Z input. Early (tube) oscilloscopes and lowest-cost oscilloscopes have sweep oscillators that run continuously, and are uncalibrated. Some higher-end analog oscilloscopes have a holdoff control. Early radar displays used adapted oscilloscopes with various inputs.