Talking about American gold coins only, there are various denominations and sizes and weights. So in order to have a "fighting chance" at finding one the first thing you need to do is find out where the various gold coins register on your computer, depending on the sophistication of your computer as far as display. I doubt very much if anyone has or is going to find modern gold coins as they are usually put away as soon as they are received. IOW, they're not carried around in pockets as in the old days. That said, it means that the gold coins that are found by detectorists are the older ones that used to be regular pocket change.
You want to calibrate your detector for the most commonly found gold coins. The first thing you have to do is get various denomination gold coins such as the pre-1900 $20 Liberty, $20 Saint Gaudens, Indian Head $5, $5 Liberty Head, $10 Indian Head, $2.50 Indian Head as examples as there are a ton more.
Here is how I calibrated my analog meter detector: I went to a SMALL local coin store and presented my case about wanting to calibrate my detector to indicate where gold coins registered. He was a friendly person and could see that I was not a threat to him. He gave me his okay and I went home and got just the control housing and coil for my TEKNETICS MARK I LTD. When I returned to his store he opened the always heavily-ocked door and actually invited me inside his office and took out 4 coins from his safe. They were the $2.50 Indian Head, the $5 Liberty Head, the $10 Indian Head, and the $20 Saint Gaudens (I could be off on the actual coins but these are close). He asked me if I wanted to try others but I declined because I was so overwhelmed by his generosity and being near the gold coins!
I told him I did not want to handle the coins. I asked him to simply pass each coin slowly over my coil a couple of times and I would write down the indicated log number on my expanded meter. I offered to pay him a small but reasonable amount for his service and he declined and just asked me to let him be the first I would show and offer any gold coins I found. I left his store exhilirated.
End of story and needless to say, I have never found a gold coin. BUT, I was ready and so was my detector. Everytime I got a signal on or near the numbers I taped to the detector, I dug.
I wrote an article about this experience and it was published in TREASURE FACTS (Lost Treasure) in the early '90s.
Silver Fox