It's a comparison of the value of a particular note (in this case an UNC DF $20) to the value of gold at the same time.
This is similar to what most companies do with their stock prices. They compare the value of their stock against the TSX index and the relevant index for their business sector. Ideally, they want to outperform the indexes that they are being compared to.
AL-Bob is stating that the value of the UNC DF $20 has seen the same proportional increases in value over time as gold has. The value of the note over the past 53 years has consistently been equal to the value of 0.6oz of gold.
Get it now? I could draw some charts and graphs, but I think a bunch of other forum members would start calling me a geek.
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BWJM, F.O.N.A.
Life Member of CPMS, RCNA, ONA, ANA, IBNS, WCS.
President, IBNS Ontario Chapter.
Treasurer, Waterloo Coin Society.
Show Chair, Cambridge Coin Show.
Fellow of the Ontario Numismatic Association.