MS Word Legacy check box selection to auto populate a field

Question

I have used the following code, to autopopulate text into a word document when an option is selected from a drop down box:

{ IF {REF DDRH \* MERGEFORMAT }="Yes" "Right Hand Machine Required"    

I am trying to replicate the process with a legacy check box, however I cannot get the text to auto populate.

{ IF { FORMCHECKBOX INFEEDF \* MERGEFORMAT } = "1" "INFEED FRONT" "" }

I have checked the bookmark names and they are correct.