GKI reading incorrect?

I am noticing that the built in GKI calculator for the app seems to be off.  For example, I plugged my readings into the app, Glucose is 83 and Ketone level is 2.0.  The app feeds me back a GKI of 13 however when I do the calculation for GKI (Blood Glucose/18/ketone level=GKI) I get a GKI of 2.31.  Can someone please address this issue or has anyone else noticed this inconsistency?