Graph - Horizontal line in scatter graph & intercept

Hi

How do you simply put a horizontal Line (example, Y=100) onto a scatter Graph

also, How do you extend a trendline so that when it intercepts at y=100, it'll draw a vertical line intercepting at x axis.. in which it returns a x value.

THanks

A sample file and a mock-up of what you are after would help.

My apologies. Here is my spreadsheet.

I have managed to create 2 series Y Lines at MaxHR and 80%MaxHR.

In this spreadsheet example. I'm trying to get the trendline to intercept(or stop) at MaxHR (y=180). And to which it draws a vertical line and provides a value representing at X axis.

How much of this is really the charting question, and how much of it is the about the necessary algebra that needs to be done before adding the lines to the chart. Assuming I understand what you are trying to do, here's how I would do it:

1) Instead of using the chart trendline to perform the regression, I would use the LINEST() function to perform the regression directly in the spreadsheet. https://support.office.com/en-us/art...a-fa7abf772b6d
2) Once I have the regression coefficients, and I perform the algebra to solve y=mx+b for x, then I can readily compute x at y=maxHR or y=0.8*maxHR.
3) From there, I can readily add lines to the chart by using additional data series, just like you did for the horizontal lines.

Is there anything I am missing? Do you get stuck on anything?