 We almost have our model complete now. The only thing we now have to decide is how much pressure in meters of sea water is still safe. We need to know the maximum values of nitrogen loading. M values. First you must understand that half times and m values are related. Remember that a small halftime means tissues fill up quickly and empties quickly. And that means it can handle a lot of nitrogen. If a tissue can handle a lot of nitrogen it has a high m value. After all that is what an m value means. And of course by the same reasoning slow tissues have low m values because they cannot handle a lot of nitrogen. During a dive there is of course always one compartment that reaches its m values first. It can handle no more nitrogen safely. We call this the controlling compartment. It controls your dive. It is the compartment that ends your dive. Let's see what happens on deep dives and shallow dives with quick and slow compartments. On deep short dives slow compartments do not have time enough to reach even their low m values. They do not matter. This means that deep short dives are controlled by fast compartments. On the other hand on shallow long dives fast compartments are not placed on the high pressure enough to reach their high m values no matter how long the dive is. So shallow long dives are controlled by slow compartments. Let's do an example with numbers so you can see for yourself. Let's look at two compartments. A fast compartment with a halftime of 10 minutes and a high m value of 25 meters of seawater and a slow compartment with a halftime of 60 minutes and a low m value of five meters of seawater. Let's first do a deep short dive to 40 meters of seawater for 20 minutes. Let's first look at the fast compartment. For the fast compartment 20 minutes is two halftimes so the compartment is 75 percent full. 75 percent of 40 meters is 30 meters of seawater. That is way over the m value of 25 meters of seawater. Now let's look at the slow compartment. For the slow compartment 20 minutes is only one third of a halftime so it's basically empty. It did not reach its m value before so we can see here that the fast compartment controls the deep dive. Now let's go on a long shallow dive. A shallow dive to 10 meters for 60 minutes. Again let's look at the fast compartment first. For the fast compartment 60 minutes is six halftimes so it's full. The pressure is 100 percent of 10 meters of seawater but that doesn't even come near the m value of that compartment which is 25 meters of seawater. Let's look at the slow compartment. For the slow compartment 60 minutes is one halftime. It is 50 percent full and 50 percent of 10 meters of seawater is 5 meters of seawater. Now remember that is the m value for that slow compartment. Therefore the slow compartment controls the shallow dive. Different models use different m values. Lower m values are safer but they give you less dive time. Low m values are usually called bullman limits. Computers often use bullman limits. This is because computers give you longer dive times already. They use the real dive profile instead of assuming the maximum depth during the whole dive. Lower m values do not limit your dive time as much when you use them with computers as they would do with tables.