My university just had a giveaway for the old electronics lab equipment that they replaced last month. It was limited to one device per person (reasonable but unfortunate), so me and my brother were able to get two things total:
- An HP 33120A 15MHz Function/Arb Generator (made in 1998)
- A Keysight 34450A 5.5 Digit Digital Multimeter (made in 2021)
I already have my own power supply, so the only thing I am really missing here is a scope, but my grandfather is planning on giving me his Tektronix scope so I should be all set with the big four pretty soon. I have done some preliminary testing on both of these new-to-me devices, and both seem to work well in all functions and both pass their self-tests (idk if that really means anything). To be honest I never thought I would get the chance to own this kind of "name brand" fancy equipment, I usually just buy the cheapest thing I can find on Amazon and deal with it if it ends up being crud. Anyway, I have the following questions:

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1) Calibration:
Keysight seems to have no record of these ever being calibrated over there (other than factory calibration), so they must have been calibrated privately. They both have stickers suggesting so. The most recent sticker on the function generator says it was done in 2024, and the most recent sticker on the multimeter says it was done in 2022 (though that surface is not very sticker-friendly so a more recent date could have fallen off). I know these are supposed to be calibrated every year, but what kind of percent error are we talking about if I happen to miss a year or two (or three)? Also how much should I expect to pay if I decided to get these calibrated?

2) General Things to Know:
What should I know before bringing these to their permanent home at my bench? I don't really know what else to ask, but I am sure there is more for me to know. Anything specific to know about these models?

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Thanks!

In the real life, 2021 multimeter will probably be OK from the point of calibration, assuming there is no malfunction. Proper calibration (done at accredited lab etc..) is quite $$, may be even more expensive itself than second-hand instrument price. Usual remedies are to verify yours against some friends/work/school instruments or known good precision resistors and voltage sources.

It may sound trivial, but the first recommendation is to read the manual thoroughly. Be careful around HID ignitors, voltages generated are usually above the instrument withstanding, and are of nasty spike/HF waveform, so could propagate without direct contact!

For home use, if you do not need a formal sticker, that is necessary if you need legal backing of your measurement accuracy (but on the other hand that could be a requirement of the insurer if it involves instruments used to ensure workplace safety, like your handbag multimeter you are using to check whether a power is present before working on something electrical)...
I think you may do calibration check yourself with stuff you (will) have (a generator, oscilloscope, multimeter).
Normally with modern instruments this usually ends up just as a confirmation they are still working correctly, unless it is really some specialty equipment, drifting away out of spec practically never happens.
The only exception here is, if something gets broken in them, but then we are talking about fixing it first and all becomes way more complex...

To get real precision ethalons, some gadgets may help:
A GPS modules use to output a precission clock signal (10MHz) when locked onto satellites. Most common GPS chipsets do, many modules sold on web do use these and have that signal available. With them you have an atomic clock precision frequency standard at home, for few bucks. Just need to set it up so it can receive the signals.

A generic quartz analog clock movement generates precise 2s pulses and can be checked (you can observe how much that clock drift over time and take that as a correction)

A common HCxxx logic generating square wave signal is good for generating exact rectangular shape pulses to check the frequency response flatness of the oscilloscope input channel.

For voltage and current you need some external standard, if you want to ensure the whole specified tolerance of your multimeter. But routine check by comparing multiple meters you have is good enough to flag the malfunction, very rarely a defect turns into just small drift, often it gets way off...

@RRK
Thank you. This multimeter's limit is only 1kV peak so ignitor pulses are certainly out of range here. It seems like calibration is probably not necessary yet.

@Medved
Thank you. I had no idea these precision frequencies were so easy to get. I will definitely try that out if I need great precision.

The precission frequencies were even easier to get in the past (at least here):
In the time of analog TV, the TV scan and color carrier frequencies were based on the national time standard. So once the TV got the signal, you can easily tap on either the deflection (the horizontal was the easiest to get, just one turn around the HV transformer and you got 100% insulated pulse output), or with a bit more complex mod into the PAL color carrier frequency.

With digital TV it is not that simple to extract anymore. Although once the same multiplex is broadcast synchronously using multiple transmitters, they need to be precisely synced together so the signal itself is precise (usually again locked to some national standard), it is not that simple to extract anything usable from that for a DIY calibration use.

But today the GPS is I think the easiest to get and the signal quality from these receivers is way superior (the phase noise, aka jitter) to the other methods, as the basic location function itself needs that precision. And because of the mass production, those things became very cheap...

@Medved - A bare 1pps (1Hz) signal from GPS receiver in fact exhibits relatively high jitter, you will have hard times extract a momentary precision of say, better than 10^-5. Especially on cheap receiver modules. More in a modern world, where GPS jamming has become a norm ( Sure, there are GPSDO's, GPS disciplined oscillators, where 1pps is used to calibrate an ovenized quartz oscillator by means of a very slow PLL. But nourishing a GPSDO is quite a rabbit hole by itself, see these long threads on eevblog, worth hundreds of pages

May be a time to look for a rubidium atomic standard in a good shape... A nice purple rubidium lamp inside, btw

The point was to use it not for measurement, but for calibration while still staying on DIY budget. For calibration the jitter is way less critical, the only thing it impacts is the time how long you need to compare the signals.
With any stand alone instrument you will always face a question whether it still works. With radio reception also carrying the timing standard you have that information: Either it is locked, so accurate, or ot is not locked and then you know that.
With GPS you know that - either it reads your position correctly (then it is clearly locked; assume you know where you are so are able to verify that), or not (so then it does not work at that moment).
Also with the analog TV: It either showed correct image, then it must have been locked, or it was not.

Of course, any radio based timing signal distribution does suffer from jitter, that why it could be using just for calibration of some more stable and cleaner generator. In that respect the GPS provides still the best quality signal, compare to other methods available for similar money.