Product review (1 stars): Faulty devices
I ordered this to replace a yellow one that I broke.  Upon arrival, I started using it as it was said to be factory calibrated.  After adjusting my pH a few times and still getting odd readings, I decided to re-calibrate it.  That proved to be a massive pain with how this device is constructed.  I tried 4 or 5 times to calibrate it with no success.  It became obvious that it was just faulty.  I contacted the company, they refunded me and sent me a replacement. I ordered another one that I had owned before and started using it successfully again.  However, I just tried the replacement pen that I got and it too isn't giving accurate results.  The first pen was off by 1 and this second one is off consistently by .5.  I would not purchase this pen if you want reliable, accurate results and a device that is easy to calibrate.  Both pens that this company supplied were faulty.