Accelerometer MPU-6050


I know that when the accelerometer is lying flat on the table I should have a reading of 1g in the z direction. However my mpu reads 0.85. I have used MPU-6050's before and all before have read very close to 1g in the z direction. Is this uncommon? Does it just need to be zeroed/calibrated/averaged? The MPU-6050 is made by Sunfounder.

Thanks in advance for any help.

It needs to be calibrated.
What reading to you get when you flip it over by 180 degrees?

Calibration overview here.