I bought a PH meter with glass electrode. I calibrated it using a buffer solution following the instructions. When I measure the PH of tap water, vinegar, or other simple liquids it initially keeps changing but eventually it stabilizes at the correct value. But I tried to measure gastric juice and it oscillates within a range that is about 2 units wide. It never stabilizes. I considered the possibility that the meter I bought is not very good, but as so far gastric juice is the only one that is showing this behavior, I though it may have something to do with the nature of the juice. Something also strange is that I have obtained alkaline values. That may happen, but it is a little strange. Any ideas? Have you seen this oscillation with certain mixture of organic compounds?