A numeric type that avoids one kind of precision problem can discard detail the report actually needs. Before converting measurements, identify the smallest meaningful difference and preserve their original representation for comparison.

Power BI's Fixed decimal number has four places after the decimal separator. Decimal number is a floating-point type with different precision limits. Changing the model type is a representation choice, not simply a request to display fewer digits. In Desktop, inspect the column's Data type through Column tools in Table or Report view.

Test a difference that a total can hide

Use two fictional measurements supplied as text: 1.23456 and 1.23454. Their difference is 0.00002, and their exact decimal sum is 2.46910. Keep those source strings and their record labels in a separate comparison table.

For an explicit Power Query conversion trial, Currency.From rounds to four decimal places and defaults to rounding ties to even. Evaluate Currency.From("1.23456", "en-US") and Currency.From("1.23454", "en-US") separately. These values are away from a midpoint tie; the expected results are 1.2346 and 1.2345.

The converted difference is 0.0001, five times the original difference. Yet the converted total is 2.4691, numerically the same as the original 2.46910. A total-only reconciliation would therefore miss the lost precision in the individual measurements.

Judge the type against the required use

Inspect the actual converted values with sufficient displayed places, then check calculations that depend on small differences, not just their sum. If the application must distinguish five-place measurements, decide whether the four-place representation is acceptable before applying it to the production column.

Conversely, if the data owner explicitly requires four-place values, document the conversion stage and rounding rule. Keep the source text available for investigating boundary cases and avoid assuming a display format establishes how conversion happened.

Repeat with a representative negative value and a value near the reporting threshold. The accepted result should preserve the distinctions required by the calculation or clearly document their agreed removal. A familiar grand total is not sufficient evidence that changing numeric type preserved the meaning of every row.

Sources: Microsoft: model data types; Microsoft: supporting procedure.