I'd like to be able to place two currencies on a chart and select a start date to see the percentage difference between them as it changes.
Being able to peg them to a set value of a fiat currency as a percentage I think would help easily know when to trade between them.
For example, select $10,000USD and see what percentage of that ETH is and what BTC is.
This...
Overlaying currencies your are interested in or invested in is a great way to quickly make decisions. By changing the thickness and colour of your lines you can highlight those you have funds in.