Problem with PH meter V1.1 SKU:SEN0161

Dear all,

I have buy PH meter V1.1 SKU:SEN0161 and i had connect this with arduino uno
I use sample code on https://www.dfrobot.com/wiki/index.php/ ... KU:SEN0161
It had display result on serial monitor
But result incorretly,
First i had calibrate with ph buffer solution 4.0
And then i test it again with ph buffer solution 7.0, but result meter is 8.99
How to for correctly result ?/

Thanks ALL