Drop-down list

One of my columns in Data sheet is currently a decimal, but i need to change it to a dropdown list with names that have a reference number, the app will show the name but i need it to use the number infact as this row is connected to other rows to do a calculation.

For instance:
Description Reference Nr.
Pool fitted with cover 0.1
Condominium pool 0.5
Therapy pool 0.65

So the App user will need to select a number according to the description, and then in the field only the number gets filled.
how do i do this?

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