What is the MS Access formula, function or query to multiply two fields that works?

I can’t figure out a formula or function or query to calculate the Volume of Liters which is calculated by:
Total Minutes X Average flow rate
See image attached. The two fields used to multiply the Total Minutes by the Average Flow Rate have a red box around them.
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cssc1Author Commented:
Sorry, to get to the proper screen just open the app and click the button "Sampling Setup" and scroll to the bottom
crystal (strive4peace) - Microsoft MVP, AccessRemote Training and ProgrammingCommented:
in a query, you can use a calculated fieldname in another expression (as you know, since you do this). On a form, however, you cannot generally use a calculated controlname in another control source; you need to repeat the equation. Therefore, this:
=[Total Minutes]*[Average Flow Rate]
needs to change

given that:
[Total Minutes] =DateDiff("n",[Sampling Start Time],[Sampling End time])
[Average Flow Rate] contains [RoundFlowRate2]

then try:

=DateDiff("n",[Sampling Start Time],[Sampling End time]) * [RoundFlowRate2]

you could also put this formula in the form record source.
You have an error in field names:
=[Total Minutes]*[Average Flow Rate]
should be:
=[Total Sampling Time in Minutes]*[Average Flow Rate (Start Flow Rate X End Flow Rate)]

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cssc1Author Commented:
Thank you both for the hep
crystal (strive4peace) - Microsoft MVP, AccessRemote Training and ProgrammingCommented:
you're welcome ~ happy to help

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