Depend on the theory:

Psychological Line is an indicator developed by Ken Muranaka.
The indicator’s values may range from 0 to 100. It is a simple indicator which shows the number of increasing/decreasing prices over a specified period; thereby is a means for deter- mining the overbought/oversold price level. The standard calculation of the indicator is as follows:

PI= n/12 ∗100

where n is the number of days(period) that the price is closed higher than the previous period.
n and the number of comparison days (i.e. 12) in the above calculation are subject to change.