With switch on engine not running the kpa value should be somewhere near atmospheric pressure. At sea level and 32*C, the kpa should be 101.3. Mine usually reads 93-96, depending on the weather.
The 100 number in the formula you found is an assumed atmospheric.
A vacuum gauge is the best method to measure the intake vacuum.
Ok, I guess ill check the kpa value with the engine off.
I don't have a vacume gauge, but I'm not really looking for ultimate performance - just seeing if there's a significant issue.