This is one of the hidden jewels of Rebrickable. The purpose of a Set Watch is plain and simple: if you want to buy a set, and you know what you want to pay for it, create a Set Watch and we will nofity you when the set becomes available in Bricklink for the price you determined. But the magic is the price history. Read on...
To show your Watched Sets: select your Profile and then select Watched Sets.
The Watched Sets page contains a standard set list with sort options (Year, Name, Number of Parts, Set Number), Drill Downs and a counter line. If you don't have any Watched Sets, you'll see a information box with the following text "You have no Watched Sets - To add watches, click the "eye" icon on any sets in search results etc."
To add a Set Watch, first find the set, then scoll down and press thebutton. Alternatively, to add watches, click the "eye" icon on any sets in search results etc. The Edit Set Watch popup dialog will open. Enter a price in the Treshold box, check Consider Used Sets if you're hunting for used sets and press the button. That's all there is to it.
But now, scroll down and be amazed.
To help you pick a threshold, Rebrickable compiles the historical cost of the selected set for the last 3 months and shows it in a stunning diagram. It includes data from all known stores except Amazon and eBay, and shows you the Minimal Cost (new and used) and the Average Cost (new and used) for each day over the last three month. If, on a particular day, the set is not available, no data point is shown. Once you discover this gem, you will use it often, just to see what the price is doing.
To delete, open the Edit Set Watch dialog and press thebutton. Be careful, there is no delete confirmation, the watch will be removed immediately.