You can set a threshold at a manually entered constant value or use a dynamically calculated value. 

• Constant: This setting will reveal a Value field where you can enter a numerical value where you wish to place the threshold.
• First: The threshold value will be determined by the first value in the series in the order of appearance on the chart. Note: the value ordering is affected by the Data Sorting setting. First value in your selected Series will be used to set the threshold based on the selected 
• Last: The threshold value will be the last value in the series in the order of appearance on the chart. Note: the value ordering is affected by the Data Sorting setting.
• Minimum: The threshold will be displayed on the smallest value in your selected Series.
• Maximum: The threshold will be displayed on the largest value in your selected Series.
• Average: The threshold’s position will be determined by calculating the mean value of your selected Series.
• Median: The threshold’s position will be determined by calculating the median (middle value) of your selected Series. 
• Percentile: This option will reveal an additional field – Percentile. You can enter your desired percent value and the threshold’s position will be calculated based on the largest value in your selected Series. (Example – if you enter 25% and the largest value of your selected series is 1000, the threshold will be displayed at 250.)