To extrapolate and find/show values on a calibration curve in Excel, you can follow these steps:

1. Enter your calibration data into Excel. This should include the known concentrations and their corresponding measurements.
2. Create a scatter plot of your calibration data. To do this, select your data and go to the "Insert" tab. Click on "Scatter" and choose the type of scatter plot you want to create.
3. Add a trendline to your scatter plot. Right-click on one of the data points and select "Add Trendline." Choose the type of trendline you want to use (linear, polynomial, etc.) and make sure the "Display Equation on Chart" and "Display R-squared Value on Chart" boxes are checked.
4. Use the equation of the trendline to calculate the concentration of your unknown sample. Simply plug in the measurement of your unknown sample into the equation and solve for the concentration.
5. Show the calculated concentration on your chart. To do this, add a data point to your scatter plot at the concentration of your unknown sample and label it with the calculated concentration.
6. Add a vertical line to your chart to show the measurement of your unknown sample. To do this, go to the "Insert" tab and click on "Shapes." Choose the line shape and draw a vertical line at the measurement of your unknown sample.

By following these steps, you can easily extrapolate and find/show values on a calibration curve in Excel and display them on your chart.