during the day the high temperature is 6 degrees more than my mecury thermometer under my patio but at night is only 2 degres warmer

if the sensor is near brick/wood/building material the radiant heat from the sun may be interfering with it and giving you a higher reading.

For the best performance from the solar powered aspirating fan be sure the solar panel is facing South and is free of dirt and debris. You can also find further tips within our Knowledge Base; http://www.acurite.com/kbase/01500_01515_Weather_Station.html You can perform a manual adjustment to the temperature if you'd like. we would recommend adjusting it by 3-4°.