This is a very old 5.5 digit multimeter with first production in 1981 or early. You can find this meter easily on ebay for $100 to $150 USD which is a real bargin for such a good multimeter. I use this meter most often for voltage and current measurement. For audio signal, this meter can easily give you a accurate AC level reading up to 100kHz. I think this is the “must own” meter for diyer due to it low cost and high performance! I have two of this.
Some internal photo of hp 3478A: This is a well design and well built unit even it is a low cost version!
