Entering Date Only When Data on a Different Cell is Edited

I am trying to figure out how to have todays date be entered in one cell when the data in another cell changes....

Take the cells I2 and J2. If I2 is blank, then J2 should be blank too. When data is entered into I2, that days date should automatically be entered into J2. If the data in I2 is ever changed, Then the date in J2 should change as well to that days date.

Purpose:
I2 is the current value of a piece of equipment. J2 is the "as of" date. So, if the value of something changes, then we could just chnage the value in I2 and we would always know that these are the values of things "as of" that date next to it.