Numeric input with unit will automatically convert number values upon unit change in a form if all of the following conditions are met:

The option 'Convert values' is checked for the Combobox (see Numeric input with unit).
The configuration for Units provides a 'conclusive link' for conversion between the units involved.

In all other cases, a change of the unit does not affect the numeric value.

The conversion logic described in the following may apply for the following contexts:

Assigning numeric values with units
Calculate value resolver in Event handling
Calculation function CALC for Calculation field

Conversion logic

In a simple scenario the configuration of the units to convert between refer to the same base unit. This is also formally given if one of the two units is the base unit..

...	Localized name	Alias	Base	Base value
	Kilogram	kg	kg	1
	Ton	t	kg	1000
	Gram	g	kg	0.001

This configuration enables conversions between any two of the units involved (Gram, Kilogram and Ton)

However, it is not a requirement to refer to the same base unit for all units in the same dynamic enumeration:

...	Localized name	Alias	Base	Base value
	Kilogram	kg	g	1000
	Ton	t	kg	1000
	Gram	g	g	1

This configuration also enables conversion between any two the units involved (Gram, Kilogram and Ton)
If necessary, multiple conversions are 'cascaded' to accomplish the task. This may involve units that are not 'Active entries' in the selection box.
As the default configuration for Time unit illustrates, this cascading approach creates transparency in enumerations for units covering a large numerical range.

Conversion and rounding

The final result of a potentially cascading conversion calculation will be rounded according to the settings for the value (see Numeric input with unit).

Example:

The value fied is restricted to 'Numbers only' and 'Number of Digits' is set to 1.
The current values read: 1750.0 'Kilogram'
After switching the unit from 'Kilogram' to 'Ton' the value reads: 1.8
After switching back from 'Ton' to 'Kilogram' the value reads: 1800.0

When the unit is changed, the rounded value is immediately stored as a change of the value.

Possible source of errors: 'Loops' in conversions

Cascading conversions introduce the risk of 'loops' or infinite cycles, as a result of inappropriate unit configurations.

...	Localized name	Alias	Base	Base value
	Kilogram	kg	g	1000
	Ton	t	kg	1000
	Gram	g	kg	0.001

Here one of the conversion definitions is 'mirrored' by another, which results in an infinite loop over kg►g►kg►etc.

The following example contains a less obvious loop:

Localized name	Alias	Base	Base value
Kilogram	kg	g	1000
Ton	t	kg	1000
Gram	g	t	0.000001

Here the loop closes across all three units in the list: t►kg►g►t►etc.

Unit configuration loops must be carefully avoided, as infinite cycles in conversions may spontaneously freeze the HTML client when a unit selection changes.