This is used HP 5350B Frequency Counter in the photographs below you can see it being used on our test bench measuring the output from an Advantech L-Band to C-Band up converter.
Our engineer explained why he preferred to use the output from the HP 5350B Frequency Counter instead of measurement using a spectrum analyzer. The frequency counter is designed to provide much greater accuracy even down a few hertz. When tuning a local oscillator or other reference frequency, measurement accuracy is essential.
A some time in the past, the directors of HP must have reached the conclusion that their business model is all wrong. They build to last, really build to last.
This HP 5350B Frequency Counter is a perfect example, it must be more than 20 years old, but it works perfectly, and so why buy another one if your tests fall between 10 Hz and 46 GHz?