MA is correct. It works the same way as mercenaries do. When they first become available, the first number is how many units are currently available to recruit - 1 in this case. The second number is how many new units become available per turn thereafter until the pool is full, which is a half unit in this case. You could retrain a unit that was greater than half strength off that, but it will use up the pool. The third number is maximum pool size, so 4 units. The last number is how much experience it has when recruited, so it should be 1 with that example.

Some units are different replenishment rates. Musketeers are 0.7, if I remember correctly. Others are 1, or even tiny fractions. Peasants seem to have a tiny tiny rate of replenishment for some reason. Elephant mercenaries are between 0.02 and 0.04 units per turn! It takes between 25 and 50 turns for one unit to become available to hire.