The running total of data recorded represents an up-to-the-moment total of the data at the time of inspection. Let's say your data is the amount of money taken in by the register of a market. The total of each sale is recorded by the data logger, and it adds the total of each sale to the total of all the others after each sale to maintain what is called a running total. If a refund is issued, that sum is subtracted, and the running total continues to be maintained.
The running total represents an instantaneous total of all the "quantities" of stuff that can be reviewed at any time during the recording period to determine what the total was at that time of review.
Here's a sample of a running total of that store's receipts:
Sale 1: $6.49 -- Running total: $6.49
Sale 2: $2.81 -- Running total: $9.30
Sale 3: $1.37 -- Running total: $10.67
Sale 4: Refund: $0.89 -- Running total: $9.78
Sale 5: $5.26 -- Running total: $15.04