How can you express improvement in percentage if figures are getting decreased?

Question

In software engineering runtime reduction is taken as an improvement.

For example, if the initial runtime was 18 hours and now it is 14min, the percentage reduction in runtime is approximately 98.70%.

But can it be expressed in % improvement? I know the below is wrong -

$$\frac{newruntime - oldruntime}{newruntime} * 100$$

But I'm not able to equate reduction% == improvement%

Answer 1

I am software developer/engineer and when dealing with optimization it helps to say the following. let's take your case: I would say

The running time is now ca. 77 times faster

This usually is well understood also by less technical people. You can also say

Because the real question here is how you define "improvement %". You could also say that with your optimization the run time is 98.70% faster. That would also work and be correct. I hope it helped.