# Comparison Formulae

Collecting performance metrics, I needed a way to compare optimization before/after numbers into some meaningful value that would impress the brass.

I don’t recall where I found these except that my Google-fu shone a light to help me get to the formulae below. I’ve had them in my notes at work for ages and today I thought to add them here for reference.

## Find savings

``Formula: (newValue - oldValue) / oldValue * 100 = percent``

E.g.: the amount of time it took to run an operation is 2348 milliseconds (`oldValue`). After an optimization, the operation executes in 842 milliseconds (`newValue`).

``(842 - 2348) / 2348 * 100 = -64.139693356% reduction in execution time``

## Find gains

``Formula: (oldValue / newValue) - 1 = x times improvement``

Think of this result as the number of times the improved performance (`newValue=842`) will run above and beyond the amount of time it took the old implementation (`oldValue=2348`). Using the values from the previous example:

``(2348 / 842) - 1 = 1.7885985748x performance gain``

Pretty good, almost a 2x gain. That means the new operation can almost run three times in the same amount of time it took the old operation. Good job! Now write a report and ask for a raise.

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