To calculate the 90% interval of an index on the official letter, we must first determine the conditions of this interval range. Only with the condition of this interval can we confirm the position of 90. The range of this interval can be time, price, volume, volume, proportion of a certain interval, etc. As long as there are interval confirmation conditions, 90% of the intervals can be confirmed.

For example, the following figure combines the judgment of time, price and volume, counts the interval within the specified time, and counts the volume ratio of a certain price interval. In fact, it is the idea of chip analysis.