The first thing to understand about the new containment cap being tested on the leaking oil well in the Gulf of Mexico, is it's a temporary measure, and is being put in place until the more permanent relief well is put in place, which will plug the oil leak.
Now that the cap is in place, it could take up to two days or longer to do what is needed to be done to successfully implement the system.
The first step, which has already been completed, is doing a seismic survey, which created a map of the rock underneath the floor of the sea in order to compare it with future surveys, so that they are sure pressure on the well isn't causing problems which can't be seen. That took at least several hours to complete.
Next, engineers from BP will shut off the pipes transferring oil to vessels on the surface of the Gulf, to see ow the cap takes the pressure of the oil pushing against it.
After that three valves which allow oil to pass through the cap will be closed one at a time.
If the oil is stopped too quickly, it could end up damaging the oil well even more, or blow the cap off the well.
What scientists want to see is the pressure readings to come in at around 8,000 to 9,000 pounds per square inch. That would indicate there are no other leaks coming from the oil well. If it's under about 6,000, they say it would mean there are leaks that hadn't been identified yet.
The purpose of the test is to see what the condition of the "wellbore below the seafloor," according to point man Thad Allen.
Each step will determine if another step will need to be taken. If nothing else is discovered, the test could be completed, and the test would be over, and the leak stopped.
That's why the range of 6 hours to up to several days has been thrown out, as each step and its success or lack of success, will change the timeframe.