By one system, this is said to consider the distance of a planet from the Sun.Planets are strongest when furthest away from the Sun and weakest when in conjunction with it. They get 60 points when at the furthest point away and 0 when in conjunction with it. As Mercury and Venus never get far from the Sun, their position is not as easy to determine.
Yet the calculations to do this are more complicated than that. Motional strength for the Sun and Moon is figured as well, but this is related to Ishta and Kashta Phala, Good and Bad Results of Planets and I have not explained it here.
This entire factor could be simplified by dividing the distance from the Sun to the planet by three and converting these to points for the superior planets of Mars, Jupiter and Saturn. For Mercury we could use 29 degrees and Venus 47, as these are as far as they get from the Sun and divide these by 60. We could consider the Moon as well, giving it maximum strength when full.