Hayanaratna 2.149

Now the strength of a planet in a fixed sign. There, at the start of the sign the strength grows. At fifteen degrees it is full. At the end of the sign it is nil. So for a planet in the first half of the sign, take the degrees already crossed. For a planet in the second half, take the degrees yet to cross. Four times these is the strength. Here is the proof. If fifteen degrees give full strength 60, what do the degrees crossed or yet to cross give? Cancel both by fifteen. The 'tryamsha' as printed are to be made four times. So it is proved. In the same way, take male and female planets standing in odd and even signs. Their strength is to be known like that of a planet standing in a female sign. This is the place strength.

Simple meaning: Place strength in a fixed sign: full 60 at 15 degrees. Take the degrees gone (first half) or to go (second half) and multiply by 4.