The Libre does have a lag, similar to Dexcom. But I used Dexcom for years and didn’t have problems with it running consistently low. Even when my blood sugar is steady and unchanging, the Libre reads lower. This morning Libre read 3.6 mmol/L, xDrip read 5.6 mmol/L, and meter read 4.9 mmol/L. The difference in Libre versus meter reading is the difference between me treating a low or not. Since I’ve been testing more often throughout the day and basing my actions off the meter results, the Libre thinks 20% of my readings are low, which is definitely not the case.