I will add the feature to my website. Should be online by tomorrow!
Most (all?) data providers rerate historical prices after corporate actions that affect prices and this is not really the correct way to do continuous valuations using the restated prices.
I forgot about the splits. But i still believe building a first version where the split is included is a good start for this feature.
Later on we can add more advance features where we can turn on/off the split
Eg. If you bought say 10 stocks at the old price, you cannot take the restated historical price with your 10 stocks and you cannot take the units held of 10 stocks with the new prices. You have to account for this via transactions to increase your holdings (for splits) by leaving the prices historically the same.