This is a bit of a tricky situation, perhaps even more so being the other side of the pond. Usually several soil samples are gathered. Then whether using a meter or the chemical method, each sample is tested. Then in most cases an average reading is taken and this is then considered to be the pH value.
I have a small test meter. Rapitest Soil pH Meter. It also can be used to check the existing light value, and moisture. Having used this in the greenhouse since the 1980's I have found it very useful if and when growing non-native subjects. It has a fixed probe, some have a short wire from the meter to the probe. Always make sure the probe is clean and dry for each test.
If very large areas are to be tested, then the tests are best left to professionals.