Since this was before bulldozer days, I can just imagine an old-fashioned horse-drawn scoop cutting down the hill on which the house was built, partially filling the creek with this earth. In another spot I find prairie soil of a different character. In one corner of the plot, tons of coal ashes were used in a mixture with some black soil and manure from a barn that once occupied the site.
All this soil history has been revealed gradually. Over a period of years I have double-dug the entire garden, uncovering everything from old barn footings to a buggy dashboard and an 1850 whiskey bottle. Incidentally, I unearthed a midden of undecayed chicken bones and rabbit skulls, which merely confirmed for me again the fact that bone (a good source of phosphate) resists decay for decades.
In this one garden, a small section filled with old eroded woods soil had an acid pH of 5.8, while the other end of the garden, where ashes predominated, tested 7.8. Obviously, if I had mixed these two to get an "average" sample I would have received a report of no value to me in working with either the acid or alkaline soils.
If you have your own test kit, however, various sections in your garden can be tested and treated individually. Even though such kits cannot be expected to be much more accurate than within two or three fractions of a point, they are much better in practical application than the more accurate electrical bridge tests of a single "average" sample.
BEST KIT FOR YOU
I recommend kits which use a special liquid that, when dropped onto a crumb of soil, turns color according to the degree of acidity or alkalinity of the sample. This can then be compared directly with
a color chart to get the reading. Some kits of this type supply a small china dish to hold the sample while others use glass tubes. A low cost unit which uses strips of wax paper is perfectly satisfactory once you learn to juggle the folded paper and read it against the chart.
Be sure to buy a unit that gives readings in direct pH figures, not in some mythical A, B, C system or in Roman numerals. Kits of the latter type are often sold cheaply or given away, but usually have to be used with a special product. Many of these products incorporate undesirable chemicals (such as aluminum sulfate used for acidifying) which you want to avoid.
Your first step in making a pH test is to get a uniform sample of the plot being tested. Don't use surface soil (roots rarely grow there) but dig down six inches. Avoid large lumps of organic matter unless you have a true organic soil such as peat or muck.