An electronic frequency counter. Used doesn't cost much. I like old HP stuff like the 5314. Just plug into the output on your phono/pre.
Lab accuracy, repeatability. Easy to get real 6 or 7 digit resolution. These days you can get used pro gear for chump change.
Lab accuracy, repeatability. Easy to get real 6 or 7 digit resolution. These days you can get used pro gear for chump change.