How to get the left x characters of a field?

How to get the left x characters of a field?

I am trying to get the first 3 characters of a given field to use in a formula for a 2nd field.  I do not see a formula/deluge script that allows for what in Excel would be Left(field, # characters).  Can anyone point me in the right direction?

For example, I have a Client Name field in a form called Clients.

I want to pull the first 3 characters of the Client Name into a 2nd field called Client ID.