By coincidence, I've also been in my lab today. My reading this morning,about 90 minutes after a light breakfast and a brew was 6.864. Unfortunately, the wife dragged me out of the uni around an hour later to take her shopping, so I can't provide a useful second reading.
These reading variations serve to confirm that salivary pH can vary not only between individuals but over a given period in a fasting individual as well. This is in accordance with documented literature available on the subject - it's nice to know we conform.
Whilst in the uni, I also had the chance to look further into the medical diagnoses from these pH readings according to some of these specialised "medical practitioners" in their journals.
You might be interested to know, newtron, that your initial pH is indicative of an individual suffering from excess gas combined with constipation. It also seems that yeasts, moulds and other fungi will be abundant in your body often leading to unexplained symptoms and infections. The good news from other "workers" seems to be that you have an abundance of "minerals" in your body, which is said to be beneficial.
Your second reading appears to indicate that you are a healthy individual!