Balancing additional units

Hi!
I would like to contribute to new unit design with a short formula.
It may help (when it works good) to determine a build costs,
 if  somebody would like to get balanced attack and defense values
 after adding new units to ruleset.

(first approach)

       build_cost = 4 * attack + 3 * defense + 8 * move_rate + 4 ;

I have tested it with civ1 and civ2 units (not used sophisticated 
statistical methods), and the results:
    
    Not works at all for:
            battleship, carrier (underestimated) and cruise missle, nuclear (overestimated)

    As i can remember it resulted the following deviance values for bild cost:
            +/- 4 shield       50% in
            +/- 9 shield       80% in
            +/- 14 shield     90% in

The following flags were treated:
        IgTer (+1 move_rate), Paratroop (+4 move_rate), Pikemen (+1 defense)

It seems that hitpoints and firepower does not influence build_cost in civ1 and civ2.
As i supect, they have a role at determining science level needed. (I will examine it
later)

Bye,
Zoltan Lakatos