I would like to request the ability to add sub-equations to the main equation
numbering scheme.

Current method: (assuming chapter 3)
sum of the forces in x-direction = 0  (3.1)
F1x + F2x = 0  (3.2)

sum of the forces in y-direction = 0 (3.3)
F1y + F2y = 0  (3.4)

In our technical journals, this type of formatting is frowned upon whereas the
recommended way of doing this would be

sum of the forces in x-direction = 0  (3.1a)
F1x + F2x = 0  (3.1b)

sum of the forces in y-direction = 0 (3.2a)
F1y + F2y = 0  (3.2b)

In this manner, the reader knows that equations 3.2b is the child of equation
3.2a and not an entirely new equation.

Any feedback would be great...