First of all - sorry for my terrible English! :)
http://www.danvk.org/dygraphs/ - good examle - multiply y-values visible (tooltips) - and one time (x-value). With line (ray)? like in this example - http://jsfiddle.net/YNS2f/188/ - it will be great for industry automatisation systems (like trendsin SCADA i mean). And if this multy-tooltip will be printable ("freezing" on mouse click, and then user can click print button) - it wiil be superb!