The corresponding ABAP domain of a quantity key figure has 3 decimal places(see note 460652). Please note that for or a quantity key figure(and an amount key figure), you can only change the number of characters(if required) before the decimal point but not the number of decimal places (see note 460652). Hence, the number specified for the fields ANDEC and DECAN of table T006(see below) has to be smaller or equal to 3.
In case a query uses unit conversion and it is necessary to get more than 3 decimal places displayed for this converted key figure, you need create a formula where you e.g. just multiply the key figure by 1. The reason why this 'trick' works is that, in general, formulas can be displayed with the maximum of 9 decimal places.
See also OLAP: Decimal Places & Rounding.
The rounding that is to be used for specific units(in a query) can be defined in the customizing (Table T006, field ANDEC).
Transaction SPRO -> SAP NetWeaver -> General Settings -> Check Units of Measurement -> select dimension "Mass" -> click on button "Units of measusment" -> Double click on unit KG
-> Setting for "Decimal pl- rounding"
=> Here you can define up to how many decimal places unit KG shall be rounded.
Alternatively, you can also completely ignore the ANDEC settings for units less than or equal to '2' by setting the RSADMIN Parameter 'IGNORE_T006_ANDEC = X' (see SAP note 866505).
See also note 2313517.
Number of Decimal Places
Table T006 has also the field DECAN. This parameter determines the number of decimal places with which this measurement unit is displayed in a query. This setting can be overwritten by corresponding settings of the key figure and query, see note 2313517 for further details.