I think your nanny might be going by what the tin says to record the water amount only, but honestly it's a bit confusing lah. The way I see it, if you're trying to track how much your baby actually drank, then 140ml makes more sense since that's the actual volume in the bottle after mixing. But if your nanny's workplace uses 120ml as the standard (like some childcare centres do for their records), they might just want consistency across all kids so it's easier to track portions that way. For breastmilk it's straightforward because you can see exactly what's in the bottle, but formula powder does add volume so the logic isn't the same. I'd just check with your nanny why her centre does it that way - could be a specific guideline they follow, or you could ask your PD at the next visit if you want the most accurate way to track your baby's intake.