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But for calibration to mean anything you will need to do it at regular intervals.
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That's partly why I think it's a complete waste of money for home/hobby use.
Unless you are running a business or have a megatastic DMM with loads of digits and you work in a physics lab it really isn't worth calibrating a modern DMM. They have been boringly brilliant for decades now and easily exceed the requirements of most professional users let alone hobbyists. I've not had to adjust any of my DMMs here at home since the 1990s. Some have never been adjusted and they are still in good agreement with each other.
Buy an old/used bench meter from one of the big names and you can expect it to retain very good accuracy for many years. If it starts to drift out of spec by a factor of two it probably isn't worth calibrating any more because it will probably be going faulty anyway.
The risk is that a hobbyist can end up (needlessly/pointlessly) calibrating a DMM every year or so like pampering a new puppy in the form of regular visits to the vet. In reality, it's the piece of test gear on a typical bench that is least likely to need any looking after or adjusting for many, many years
