iam using ph instrument lab india make.3ponit and 5point.in calibration time 3point slope will come 98.89and 96.87.that limit is 85 to 105.what basis slope will come.any calucalation between them.5point wiicome slope 99.89?why 3p0int came 2 values?

iam using ph instrument lab india make.3ponit and 5point.in calibration time 3point slope will come 98.89and 96.87.that limit is 85 to 105.what basis slope will come.any calucalation between them.5point wiicome slope 99.89?why 3p0int came 2 values?