Why NSE,BSE values are almost same for a share

Hi

This may be stupid question ..
NSE and BSE are different exchanges even then if a share exists in both the exchange why the share price,its variations,trend, etc are almost identical to each other with only a slight change ??

simple thing i may think of is that if at all there is gap between the both exchanges the arbitrage will be done by traders and the prices will become similar again..its like equilibrium..

it is like buying bata shoe from two different stores

Arbitrage will help only in the difference is sufficient enough to breakeven and make profits. They cannot arbitrage for difference of 5 or 10 paise because transaction costs will outweigh the potential profits. The prices are same because it is the same delaer or market maker who is executing orders on both the exchanges.