Which setting is necessary within data validation to restrict entries to a range of decimal numbers?

To restrict entries to a range of decimal numbers within data validation, the appropriate setting is to select "Allow: Decimal." This setting specifically enables users to enter values that are numeric and can include decimal points, thus allowing for a wide range of values, including fractions or precise measurements.

When setting up data validation, the "Allow" option can be adjusted to determine what kind of data users are permitted to enter. In this case, selecting "Decimal" ensures that any input must be a number that can have decimal places, which is essential for scenarios like financial calculations, scientific measurements, or any context where precision is crucial.

Other options, such as allowing whole numbers, text lengths, or lists, do not cater to the need for decimal inputs. Whole number settings would prohibit decimals entirely, text lengths would restrict entries to character count rather than numeric values, and lists would limit entries to predefined selections, which undermines the desire for diverse numerical entry with decimal precision. Thus, choosing the option for decimal is the only way to fulfill the requirement for specific numeric data entry with the ability to include decimal notation.