I’m not sure if I understood correctly.
Change the field type of the below field from calculation to number or text.
Use a script trigger to change the value: trigger when the above field is modified. the script will enter a value (i.e.1.5) in the below field
You can associate a drop value list in the below field and enter a value from the list (i.e. 2.5).
Thank you. Will try that tomorrow. Thanks for help.