# This article shows you how you can force weighting targets to add up to 100%

Weighting requires that the table(s) of **Targets** add up to precisely 100%. Where they do not add up to precisely 100%, you will receive the message **The sum of percentages in the target table does not add up to 100%** and will not be able to proceed.

Causes of this error include:

- Human error (e.g., numbers that add up to 90%).
- Rounding error in tables (e.g., numbers in a table that add up to 101%).
- Rounding errors due to the precision with which numbers are stored and computed on computers (i.e.,
*floating point errors*). This is the hardest type of error to spot, as often these numbers appear to add up, but, when copied and pasted into another program, do not actually add up.

## Method

The most straightforward way of ensuring that weights add up to 100% is to:

- Copy and paste the numbers you have entered into Excel (note that there are copy and paste buttons above the table).
- In Excel, create a new table which uses formulas to link back to the previous table, but using the
`ROUND`function. In the example below, the data is rounded to 5 decimal places. You can do up to 12 if you want to be super-precise, but it is unlikely to make much of a difference. - Select all the cells in the table of rounded numbers (i.e., the right-most table in the example below), and check that they add up to 100%.
- Manually change one of the numbers in the table so that it does add up to 100%. Excel shows you this in the bottom-right corner of the screen.
- Select the table of rounded numbers and paste back into Displayr.