You’re trying to reference a calculated column (Miles) that exists only in the view of your first table, not in the underlying metadata. rows.Miles doesn’t work unless Miles is an actual property or calculated during grouping.
You must re-use the (odometerEnd - odometerStart) calculation directly, because Miles is not a real field.
On the phone, so can’t test it, but can you try this:
```dataview
TABLE sum(odometerEnd - odometerStart) AS "Total Miles"
FROM "CASA Mileage"
WHERE file.name != "CASA Mileage"
WHERE file.day.month = date(today).month - 1 AND file.day.year = date(today).year
```
Cheers, Marko 