OSCILLOSCOPE

An oscilloscope is an instrument for visualising electrical signals. Modern oscilloscopes are based on fast analog-to-digital converters, a microcomputer and a digital display. They are remarkably cheap compared to their analog predecessors of fifty plus years ago. 

The Tektronix 422 is a dual-trace 15 MHz portable oscilloscope, intended for field work. It has space for a 12 volt battery pack. This AC/DC model sold for $1625 in 1966. My 422 was built by Tektronix in Heerenveen, the Netherlands. It works as if it was its first day. I also have a Tektronix 454A dual-trace 150 MHz oscilloscope on a cart.

In the 1950s the Philips company produced a series of small single-trace oscilloscopes. I have two GM5655 models in working order.