What is your favorite piece of equipment to use?
To state the really obvious, it depends what I am doing at the time!
But as for the question
i don't know how i ever managed without it
that probably applies to most things at one time ot another.
Having been into radio/electronics as a hobby for about 50 years, it is amazing how much messing about you have to do when you dont have the ideal bit of test equipment to hand.
One example sticks in the mind, I was trying to build a crystal calibrator, a device for generating accurate frequencies for setting the calibration of shortwave receivers.
I had a 100khz crystal oscillator which worked well, but wanted to extend it to generate signals at 25 and 10khz, using 7490 TTL dividers.
It worked, sort of, but would give signals at 50khz intervals instead of 25, and 20 khz instead of 10khz. I gave up on it.
Some years later after I had an oscilloscope, I re-visited the thing and found the problem in an instant. The problem was not with the divider chips, where I had been giving all my attention, but the crystal oscillator.
The oscillator output was distorted in a way that effectively gave a 200khz output rather than 100khz. Listening on a receiver, there were signals every 100khz, but in the time domain it was a 200khz signal and the 7490s switched on the 200khz glitch!
One thing that I have noticed over the years is that simple bits of equipment which at the time were in the category of "how did I manage with out it?" are superceeded and remain unused as more sophisticated equipment comes along.
Example, in the early 1970s I built a GDO (Grid Dip Oscillator, google it if you dont know what it is), a really usefull bit of kit for setting up tuned circuits and finding the frequency of an oscillator.
But since then, a spectrum analyser and tracking generator can do the same thing and much more. The GDO just sits in its box gathering dust.
JimB