I have noticed in my nearby gym that they have machine equipment like: lat press/lat pull down/machine fly/etc. all of which have their successive weights as: 5kg, 12kg, 19kg, and so on.
On the other hand, the dumbbells are in steps of 2.5kg i.e. 2.5kg, 5kg, 7.5kg, etc.
Considering that the same human body exercises on both types of the equipment, why does one set of equipment increase in 7kg and the other in 2.5kg? What factors would make one number a better fit for one type of exercise, and the other for the other type?
I personally find the number 7 an odd step to choose as it is a prime number and has a non-terminating decimal expansion (1/7=0.(142857))