Automatically highlight a point on a line graph

[HC1994]

Suppose I have a set of data of price trend that is plotted on a line graph, labeled by date.

I want to be able to input a specific date in that range, and the graph should highlight the data point on that date? Specially, I want to be able to draw a line down (This is bonus, as long as I can somehow highlight that point in anyway).

Another application is, if I have a range of stock prices on a specific day, I want to be able to find the data point of a specific stock on the graph.

Please let me know if this is clear enough.

 

[01-7700]

My solution is to create a data series and set the format to column. The value of that data point could be set to the max of all values and using a formula, only show the column on the input date.