Interested in selling some gold jewlery, one piece is equal to an ounce of gold. What is the reference to "penny weight" in selling gold?

Pennyweight is a unit of measure in the troy system of weights. It is used to weigh gold, silver, platinum, coins, and most jewels. The pennyweight was once the weight of a silver penny. Today it is standardized as one twentieth of a troy ounce, or 24 grains (1.6 grams).

Just for further explanation.
At the current price of gold which is very close to $1,200 an ounce.
So, 1/20 of 1,200 = $60.