I understand what are the outs and pot

odds ... etc

but given current hands and without the knowledge or others' hands,

is there a systematic method or an equation to compute the equities without using the calculator?

In real life situation, when using the equities calculator is impossible, having the ability to calculate the equities would be a good strategy.

I somehow think that "counting cards" like the way you do in

Blackjack could be modified and be implemented to calculate the equities though....