there are so many factors that can influence the price... this what you say 1600-1800 is quoted in dollars. Is dollar an objective measure of real value? If u are talking about real value put there something differnt like oil to gold or gold to land or food, why are you thinking about dollar. How is the outcome then ?
Ok, but 2 years ago people knew what you said , when they took the price from $900 to $1900 in 2 years lately or sth like that, they were aware that gold is not the most practical and needed thing in today's world. But they thought: hey, if u value a car for 100.000$ how come you give 3kg of gold the same price tag. There is not too much gold in the world. If you made a ball from all the gold in the world it would be only sth like 25m tall (!) Some may consider it a currency, a currency that no one have a power to create more.