Outlook Form - Yes/No event date

I've made a custom form that has several checklist fields (YES/NO) and to them I've associated formula films in order to get the date they are checked. unfortunately the formula fields are not working. Whenever one is checked all the dates are update to the same

What I have: Check1

• Yes/No field Date1
• formula (IIf([Check1]=True,Date(),"") Check2
• Yes/No field Date2
• formula (IIf([Check2]=True,Date(),"")

and so on

The idea is for the date fields (Formula fields) return the date for each check and not to update all every time an yes/no field is checked

I seem to lack the knowledge to overpass this problem

Can you help?

Thanks!