Here is more detail on how to do this, suppose your data is like below:
Column B is on set of lab results, column C the second lab result, Column D
the formula =C2-B2 to calculate the difference
A B C D
Name Lab1 Lab2 Diff.
Test1 61 31 -30
Test2 87 47 -40
Test3 69 97 28
Test4 27 47 20
Test5 72 36 -36
Test6 15 6 -9
Test7 74 80 6
Test8 31 58 27
Test9 86 58 -28
Test10 1 61 60
Test11 70 60 -10
Test12 67 51 -16
Test13 53 43 -10
Test14 43 12 -31
Test15 18 42 24
Test16 15 67 52
Test17 89 77 -12
Test18 40 32 -8
Test19 58 49 -9
Test20 48 38 -10

Chart column A and D with a line chart.

Double-click the series and on the Patterns tab set Lines and Markers to
None, and on the Data Labels tab turn on Values. Click OK.

Double-click any data label and activate the Numbers tab, choose Custom and
enter the following format:

"+";"-";0

--
Cheers,
Shane Devenshire


"martina" wrote:

Can one make a dot plot chart using chart wizard. This chart will have 40
data points. The Y axis will be split in the middle with the upper half being
"+" and the lower half being "-". The median line on Y will be "0".

The graph will demostrate the differences from one number compared to a
second number.

Thanks