I'm downloading historic data for Brent Crude volume using intraday summaries. This gives me raw data for every single volume update. Sometimes a few per second. I'm then summing these myself across a day to find cumulative volume up to that point each day. This has seemed fine but where I've started to analyse my realtime data, where I actually use the content field 'ACVOL_UNS' to download the cumulative volume every minute, I've found that they don't match up.
The question is, am I doing something stupid here?