I use an only Ph tester from BlueLab. It needs 4.01 and 7 to calibrate, pictured.
Obviously use what your pen says but a couple of times on calibrations its meant to ask for 4.01 the first calibration (you can use 10 if you regularly expect to be testing 8+)
Anyway you go first with the low (4.01) or the high (10) and it recognises the wide discrepancy and calibrates and second dip you give it the 7.0 to finish.
Mine has got confused before. Reading about it I think its because I wasn’t careful enough about cleaning it and soaking it in KCI solution for at least a few hours before calibration.
It gets confused. Who doesn’t!
I’d suggest a thorough earbud/q tip clean and of you can a soak in KCI solution first. If not - try the clean and re test.
Hope that helps!
Nick