Hi TolpuddleSartre,
By my understanding, it is.
I can see no proof from you to show that it is not.
See the attached screenshot of the serial monitor, each time 1000ms passes i remains at 0.
Hi Speklap
You don't update currentMillis.
What happens is
i = 0 -> the if statement is correct -> previous = current
i = 1 -> current - previous is always zero -> if statement false
i = 2 -> if statement false
...When you finish the for loop, then your currentMillis gets updated.
Try to rewrite this.
From the screenshot you can see currentMillis is indeed updating.
Regardless I did try moving the unsigned long currentMillis = millis();
around in the program however this did not help.
Thanks for the input guys.
Still trying to figure this out. 
