Limit data validation values to a 1 point margin in 3 different cells

I have a section of my program that asks for board scores (point value is 6-10 in increments of .5) I have set up a data validation so that users can only enter those specific values. Problem is, none of the values can be more than 1 point from each other. (the part I have yet to figure out)

Example, if the first value is a 6.5 the second is 7.0 and the third is a 9.0, I need the data validation to display an error because the 9.0 is beyond the one point spread.

Summary: Display an error message if any of the points are more than 1.0 point from another.

Thanks, you guys have always been great at hepling me!

It would be easier to answer if you post a sample workbook showing which cell containing validation are to be compared.

Based on your sample file, without wanting to alter J52:J60 (unknown knock-ons) you could perhaps do something like

H52:
=IF(MAX($H$51:$H51)=MIN(10,MIN($M$12:$M$14)+1),"",MIN(10,0.5*(ROWS(H$52:H52)-1)+MAX(6,MIN($M$12:$M$14)-1)))
copied down to H60

Then highlight M12:M14, selecting M12 first, and apply a Validation List of:

=OFFSET($H$52,,,COUNT($H$52:$H$60),1)

Note: I wasn't entirely clear on the rules and have assumed that when first value is entered, say 9 the next value could range from 8-10, if 8.5 is selected the 3rd selection options can only fluctuate from 7.5 to 9.5
(ie the +/- is based on the MIN)

Post late, but a similar solution to DO, only w/o the helper column.
I assume you list of numbers will remain fixed, but you could name the range so Excel will track it if you move it.

Data validation formula, list option:
=OFFSET(INDIRECT(ADDRESS(MATCH(MIN($M$12:$M$14),$J$52:$J$60,0)+51,10)),,,3,1)


Edit: in testing the formula by DO, you can get a spread of points greater than 1-point. Based on the OP's note in the workbook the total spread from lowest score to the highest should not be greater than 1-point.