Hi Hal,
This topic is a frustrating one. pH is an important aspect of growing plants but good, low maintenance, and affordable meters are difficult to find. The really cheap ones are worthless because of false results. Most of the others require maintenance of the probe and recalibration between uses. There are a lot of meters available due to the popularity of hydroponics and any of the standard companies like Hanna Instruments have many models to choose from. There are also laboratory meters that are expensive and unnecessary. In fact, you can get an idea of pH just using the cheap paper strips that turn color but these are not that accurate.
There are meters that are made for and intended to be used in agriculture and horticulture. I like these the best - they are easy to use, low maintenance, and give consistent results. pH is only one of the measurements needed to grow plants - soluble salts measured by electrical conductivity in another. Anyway, the agriculture meters that are well regarded are those from Kelway and Myron L Corp- see
http://userweb.cybernex.net/kelway/ph.html and
http://www.myronl.com/products/agrimeters.htm for details.
Another aspect of this question is whether you are going to be testing soil or water or both. If it's soil then preparing a slurry properly is important unless using one of the meters mentioned above that can be stuck directly into soil.
Let us know what you try and how it works.
Charlie
