Apply only one calc rule in cart

[boris_prv]

Hi. I have installed Virtuemart 2.0.26d version.
For expample I have Calc Rule for Shopper group (-5%) and I have another cal rule for product. Then if I logged Like shopper that have calc rule (-5%) and I buy product with another calc rule than apply both rules. Can I apply only one becouse its normal situation in ecommerse?
And other similar question: now if I have two or more calc rules they all apply for items. Can I  apply only one in this situation too?
Thanks.

[K&K media production]

You must setup the product discount rule to another shoppergroup than the other cart rule.

[boris_prv]

I create the solution. I write a plugin. If calc rule decrease the price I leave the rule that gives more discounts - other delete.