Date and time arithmetic

Note the use of date and time arithmetic to calculate the elapsed time between readings. The formula in cell B7 is ... 

If you keep in mind that Excel stores dates and times as date serial numbers, performing date or time arithmetic is simple. For example, in a kinetics experiment you may have a table of times at which data points were recorded at irregular intervals (Figure 3-15). To analyze the data you need the elapsed time from finitial- Subtracting the time values from the initial value yields numbers that are decimal fractions of a day and are converted into minutes by multiplying by 24 X 60. The formula in cell B2 is =(A2- A 2) 1440. 

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