Convert power readings to energy readings
The reading of energy in the top of the final column is accumulated energy taken from power measurements that occured prior to this table. The 2nd energy reading is 1 watt hour larger than the previous reading.

From that and given that the time interval is 30 seconds, I calculate that the average power over that time period (30 seconds) is 120 watts i.e. 1 watt x 3600 / 30.

Does that help?

The fact that the power reading at 54:52 is 123.45 watts doesn't mean that it remained stable at value throughout the previous 30 seconds but it may have and the energy reading may not show enough decimal places to register this slight discrepancy.