Question about finding electric field using slope on excel

[MaryCate22]

Homework Statement

I have a list of data, positions and measured voltages at each position. As part of my lab analysis I have to find the electric field at each position. I know that the slope of a potential versus distance plot is the electric field, but I have no clue how to find not the average slope, but the slope at each position in excel.

Homework Equations

In my lab handout says the most useful formula for finding slope from data is dy/dx=[y(x+h)-y(x-h)]/2h

The Attempt at a Solution

My question is basically how to find the slope at each position. How do I make use of the above formula in excel?
My worksheet is attached. I'm sorry if this is the wrong board for this type of question.

 

[mfb]

How do I make use of the above formula in excel?

Let h be the step size of your data. Which means y(x+h) is one cell away from y(x) and y(x-h) is one cell in the opposite direction.