Peru issued these nice gold coins as Trade Coinage, i.e., coins to be used outside of Peru herself. The pattern is the same, but the size and gold content are different, as follows:
1/5 libra: 15 mm diameter, 0.0471 troy ounces of gold
1/2 libra: 19 mm diameter, 0.118 ounces gold
1 libra: 22 mm diameter, 0.235 ounces gold
To find the value of your coin, first multiply its gold weight by the current price of gold. For instance, today's gold fix, according to web site kitco.com, is $1178 US dollars per Troy ounce. For a 1 libra coin, the base value is 0.235 x 1178 = $277 US dollars.
All dates of this coin are equally valuable -- there are no dates that are worth much more than other dates -- although coins dated before 1930 tend to be slightly more scarce than those after 1930. For coins that are in superb condition, fully uncirculated or nearly so, you can add a small premium to the base value to account for collector appeal. The coin in our picture shows 'normal' wear and eye appeal, so no premium should be added. If the coin knocked your socks off with superb luster and appeal, you might add $50 US dollars to the base price.
NEVER CLEAN A COIN. CLEANING RUINS VALUE.
Remember that when speaking of precious metal like silver and gold, 'troy ounces' and 'ounces' mean the same thing; 'troy' is understood.