This equation governs all speed in swimming. Speed in the water depends on how far a swimmer can travel on each stroke, and how quickly that distance can be covered on each stroke.
In TI (and in swim training in general) we will use the term Pace because it refers to something we can easily relate to – how many seconds does it take to cover 25 meters, 100 meters, or 1000 meters. Pace is just the inverse of Speed, mathematically speaking.
And in our training, SPL and Tempo are also easy to measure and use in our thinking.
A certain SPL x a certain Tempo will always result in a certain Pace. So, in order to reach a desired Pace for any event, you need to train to hold a specific SPL and Tempo combination that is appropriate to your body dimensions and appropriate to the swimming event.
You may refer to the Pace Combination Chart for Open Water and the Pace Combination Chart for 25m Pool.