This is a follow-on from tip 1 on Data Validation

When adding data validation to cells containing percentages, there is a little trick you need to know. If you're calculating a proportion: 100% being everything, 0% being nothing, you need to set the data validation to DECIMAL with range 0 to 1.

Why ? - Because in this case the percentage is actually a fraction of 1

Training Video - Data Validation for percentages