User-defined atrribute creation in Aris.

Hello,

I am trying to create a user defined attribute in Aris. However,I want to create an attribute such that the user can enter some data,then select its unit from the drop down box. For example:

Here,Maximum orientation time a in-built attribute where the user can enter a numerical value for the timethen select whether its unit is seconds/hours/days etc from the adjacent drop down box. How do you create this in user-defined attribute?

Thanks in advance

Anaya