I have a 9 1/2 counts multimeter, and when I calibrate DACs I need all of those. The last two digits are a bit noisy but hey. There is no rule of thumb, except

I have a 9 1/2 counts multimeter, and when I calibrate DACs I need all of those. The last two digits are a bit noisy but hey. There is no rule of thumb, except that people should understand that I can give the illusion of precision to every measurement by capturing crap. Those 32 bits on your laptops onboard audio interface are the real banger, when even the least significant digits in 16 bit mode are filled with electromagnetic interference and noise from the power rails. Real, actual precision is way more hard to reach and you will know when you reach it, because you will have spent a lot of money on the way. Whether you need it, or wield it correctly is a different story.