The 7403N oscilloscope was introduced in 1971 and phased out by 1975 being replaced by the faster 100 MHz 7603N. The "N" nomenclature indicates it does not have on-CRT readout. The 7403N takes two vertical and one horizontal plug-ins. The museum has a military version AN/USM-281C which is a ruggedized 7603N on display. It has different vertical plug-ins than the 7A15AN normally shipped with the militarized version.
These ads appeared in the July 1971 issue of Wireless World advertising the 7403N Oscilloscope. The £1024 price is roughly equivalent to $15,000 in 2017 dollars.