Try doing it like this (see screenshot).
Does that give you what you need?

For your information: I used the Absolute Value (Abs) because the expression returns a negative number. This makes it positive.

You need to change GROUP BY to WHERE, if you only want that column to be a criterion and not part of a group.

Thank you Kevin R and Kevin Y - this now works fine. Can I ask one other question. If I set up a report with the information received by the query, is there a way that I can automatically show in the header that it shows the start and end dates. I will attach a screen shot of what I mean. Thank you

Instead of parameters consider getting your date values from a couple of Form fields. This will make it much easier to plug the values into your Header Label.

Hi Kevin. I understand what you are saying, but not sure how to do it. Do I need to set up a different query without the parameter fields and instead enter those dates on a form, but how do I then get it to do the sums?

Hi Kevin. Realised how you use the Forms!FormName!StartDate etc, but it then doesn't show me a total when I run the query.
The original query that you sent was: Number Seen for Dates: Sum(Abs([DateSeen] Between [Start Date] And [End Date])). When I substitute the Forms! etc. it looks like this: Number Seen: Sum(Abs([DateSeen] Between [Forms]![BridgeleySubMenu2ReportF]![StartDate] And [Forms]![BridgeleySubMenu2ReportF]![EndDate])) Looks right to me but it doesn't give a total. The form where I am entering the data is open. Any suggestions please. I submitted it as a jpg to make it easier to read

Let me know if the screenshot below helps.

Hi Kevin. Thank you so much for your time and effort for me. The result is what I want. Can you clarify a couple of things for me
1. Do I create a blank form called AssistanceGivenF?
2. The actual count is based on the PersonID. Each person may have multiple assistances give (AssistanceID). What we need to know is how many different people (personID) are seen in that specified time - so in the last line of your code, should it have PersonID.assistancegivenT so it counts the Person ID.
Thanks again for all your help - look forward to hearing from you

Hi Kevin. Can you tell me if you set up the form AssistanceGivenF with the header and label first. When I try and run the code you sent, I get this error....Object doesn't supportthis property or method and this line is highlighted in the vba code
HeaderCaption = "Number Seen from " & StartDate & " to " & EndDate
Not sure where to from here. Thank you