An 'at most useful' purchase is an order distributed by a client to a broker where no certain training is provided on cost. Also referred to as a 'market' purchase. Therefore, an instruction to 'buy 500 stocks in business X at the best' implies that the broker will finish the purchase within best cost available at enough time, as well as the customer can't be certain what that price is going to be. On the other hand when a customer locations a limit order he actually dictates the price from which he is willing to buy or sell, therefore the agent can just only make a deal in the limitation provided.
When an agent is told to purchase or offer in the most useful cost regardless of what the trend.
beneath the best of conditions
Exchange of gas through the walls of the air-sacs, almost devoid of blood-vessels, can at best be much restricted.