Well, that's one approach, but it can be difficult to be exact. But if at all possible, I try to use gram measurements, as explained here
http://cheeseforum.org/forum/index.php/topic,5669.msg41416.html#msg41416for normal starter cultures, if you over or undershoot, the cheese will should come out OK. Not consistent, but acceptable, especially if you monitor acidity. For mold cultures and specialty cultures that need such a small amount per 100 liters, adding too much or too little can make a big difference.
Using DCUs and gram measurements is a much more consistent approach. If you're using teaspoon measurements and want to be consistent, it's better to use mother starters, as Sailor has posted about in his photoessay thread.