Nifty Option Pricing

Dear Members,
I am a regular trader in Nifty options. For last few months i have been observing some change in option pricing for call options the price is not increasing much along with the nifty moving up even though it is having high volatility and at the same time when nifty lowers few points the price is falling rapidly more than nifty. what would be the reason for this type of pricing.

I request anyone to suggest me a best black scholes option calculator.

Thank You.

I believe it was all about implied volatility IV. Please remember direction of the underlying (delta) is only one greeks' factor affecting the option price. IV is a very important factor affecting the time value of an option. Even if there is no movement of the underlying, the price can be changed because of the IV. For example, if the market is very slugguish, people will try to sell IV and push the prices of options down.

Actually, I was an option maker maker.