Final answer:
Tableau calculates the median by finding the average of the two middle values when there is an even number of data values, or by finding the middle value when there is an odd number of data values.
Step-by-step explanation:
When a data set has an even number of data values, the median is equal to the average of the two middle values when the data are arranged in ascending order (least to greatest). When a data set has an odd number of data values, the median is equal to the middle value when the data are arranged in ascending order.