Distinguish volume from OBV
Volume shows the amount traded per bar. OBV adds that volume when the close rises above the previous close and subtracts it when the close falls. An unchanged close leaves OBV unchanged. This classifies volume by close direction; it is not measured bid/ask delta.
CVD accumulates the available delta
When the source supplies delta, PRAETIR sums those contributions within the chosen RTH or Globex session. Synthetic contributions of +40, −10 and +20 produce CVD readings of 40, 30 and 50. The sum restarts at the session reset. A different reset or incomplete history changes the comparison.
Recognize bid/ask, mixed and proxy data
The “Proxy” label identifies an approximation, rather than a complete record of bid/ask executions. Use the same data basis for comparisons and check whether its label changes between views.
“CVD · BID/ASK” identifies fully covered delta data, “CVD · MIXED” a mixed basis and “CVD · PROXY” the approximation. Preserve that label in your trade evidence. Comparing measured delta with a proxy could otherwise appear to reveal a market change when the data basis has changed instead.