On day one, the OBV is simply the daily trading volume. For day two however, you can calculate the OBV by seeing whether the closing price is higher than it was on day one. In this case, the closing price has risen by £5 on day two. As a result, the OBV can be calculated by adding the daily trading volume of day two to that of day one – 10,000 to 14,000 – which would give you 24,000 as the OBV for day two.
If the closing price is less than the previous day – as shown in the example on day four compared to day three – then you would subtract the daily volume of day four from the OBV of day three. This means that you would take 10,000 (the trading volume for day four) from 36,000 (the OBV on day three), which gives an OBV for day four of 26,000.