I had just optimized some code, and was about to say that it was “20% faster” when I realized I wasn’t really sure of what that meant. I said “takes 20% less time” instead, but now I have to know – what is “20% faster”?

(This may seem silly, but there’s a practical side as well. You find these kinds of measurements all over the place, particularly in product marketing. Just Google some of these phrases and see for yourself.)

Let’s start with something that seems obvious: length. If our old rope is 60 inches long, this is how long the new rope would be, depending on how we describe it:

• as long – 60 inches
• twice as long – 120 inches
• half as long – 30 inches
• three times as long – 180 inches
• one-third as long – 20 inches

Makes sense, right? What if we use the word “longer” instead of “as long”? That is, how long would the string be if it was “200% longer”? Twice as long, i.e., 120 inches? That seems reasonable, until you consider what “50% longer” would mean:

• 50% longer – 1.5 times as long – 90 inches
• 100% longer – twice as long – 120 inches
• 200% longer – three times as long – 180 inches

Let’s make things a little more complicated. What about the word “short”? How long would the string be if it was “half as short”? That’s a tough one. Many people would use that phrase if they thought that the old rope was “short” already, and they would mean that it was “half as long,” i.e., 30 inches. But what if we said it was “twice as short”? That’s got to be “half as long,” too.

The difficulty here is that we don’t have a number that gets bigger as the rope gets shorter. The only logical thing to do is to make “short” the inverse of “long”:

• as short – as long – 60 inches
• twice as short – half as long – 30 inches
• half as short – twice as long – 120 inches
• three times as short – one-third as long – 20 inches
• one-third as short – three times as long – 180 inches

Those figures just seem weird, so it would probably be best to avoid that usage. Of course, we wouldn’t be done unless we considered “shorter.” How long would the new string be if it was “50% shorter”? We’d better just subtract that percentage from the original length:

• 50% shorter – 30 inches
• 25% shorter – 45 inches
• 75% shorter – 15 inches

By that logic, “100% shorter” wouldn’t make much sense, since it would be 0 inches. “200% shorter” makes even less sense. Again, you probably want to avoid using “short” or “shorter” when describing relative measurements.

Well, that’s all for now. Tune in next time for the next exciting installment of “Relative Measurements in English,” where we’ll discuss other forms of measurement, and finally decide what “20% faster” really means!