Read percentile value at any point on the X-axis

[Thormenting_Slumberjack]

I have a plot with set phi grain size values on the X-axis, and percent on the Y axis. The plot is made by calculated cumulative values.

What I need is a way to determine what the grain size value (X) is at any point (n'th percentile) on the "cumulative curve" (see picture). I should add that there is a ~ 0,25 (~.50 in the picture) jump between each value on the X axis.

I hope someone can help me. I'm working on my thesis with a dead-line running towards me..

 

[AlphaFrog]

There are no functions in Excel to read a value from the plot line on a chart. You can, however, calculate a value from your data.

The two methods I know of are

1. Best fit Trendline formula
2. Linear formula from the two bracketing data points.

Best fit Trendline:

• Right-click on the plot line on the chart and select "Add Trendline"
• Type: (for your data) 6 order polynomial
• Options: Checkbox "Display equation on Chart"
• Ok
  Use the displayed equation in a cell formula to calculate for an unknown.

Linear formula of bracketing data:
Say you have data points for 50% and 60%. You want to calculate for 57%
=FORECAST(57%, 2_Cells_known_Xs, 2_Cells_known_Ys)

2_Cells_known_Ys are the two cells with 50% and 60%
2_Cells_known_Xs are the two cells with 50% x value and 60% x value
Note: you can transpose the known Xs and Ys in the formula to calculate for an unknown Y (instead of X).

 

[Thormenting_Slumberjack]

Thanks for the reply! I will look into it right away. Too bad there isn't an easier way...