how do I calibrate ph 6.86?

[GrowMyOwn]

my ph meter does not have 6.45= 3 digit display just a display that reads 6.4
so my question is how do I calibrate this ph 6.86 solution?do I round it up to 6.9?
I don't have a thermometer yet but I should have one tonight

the solutions I have are 4.0 and 6.86 with a cheap 2 digit display
thanks for the help

 

[Gorhad]

Secondary test would be either a NPK and PH soil (if your medium is soil) tester or to be honest here in florida , i have a pool service so i test my water PH with the same pool water test kit i have and then verify it with the analogue one i have and they are not far off. Put it this way i havnt had too many probs with acidic pools in the last 15 yrs or alkaline for that matter lol

 

[GrowMyOwn]

so I should just adjust it with the screw driver untill it says 6.8 or 6.9?

 

[MacEFL]

The instructions that came with my cheapy said to use the 6.86 and adjust meter to 7.

 

[GrowMyOwn]

thanks tester came with instructions but the solutions were purchased seperately,but instructions says to tune it to 6.8