Copied from another forum................Frequency is the cycles of resonated signal that is sent by the oscillator circuit, down into the two coils. One coil is the Tx coil, the other coil is the Rx receiver coil. The ground, which is the receptor of this frequency, can be in many different conditions, at the very moment of the transmission of the freqency.
For example, the ground can be water saturated from a heavy rain, frozen from extreme cold, dried out dryer than a camel that has been in the desert without water for two weeks, covered with snow, covered with sand, gravel, clay, cement, and so on.
Electronic parts can be brand new, can be old, extremely cold, newer superior kinds of electronics compared to older vintage kinds of electronics, so you can see the variabilites here...
The simpliest form of metal detector requires merely looking at the amplitude changes coming to a detector into its Rx coil, and these can be shown by a simple analog needle meter, or a more complex meter.
Now when you begin to consider the more complex TID meters, which not only tell you the conductive characteristics of the target, but its depth, you add to the complexitity of the detector.
You see here with target identification, we are not concerned just with the amplitude changes, but are now looking toward something else, phase changes of the received signal in the receiver circuits as well...
Also each metal in the ground has its own resonate frequency, according to George Payne, and the closer you get the oscillators frequency to the particular target you are in search of, then that changes things in the view that you are looking toward. For example if you are seeking just gold, or seeking silver, or seeking any kind of coin, or seeking any kind of jewelry, all of these things must be taken into effect in reaching a conclusion that you are desiring... The closeness of the target to the coil also comes into perspective.
Then we must consider the time period that the targets remained within that soil, and we must compare the kind of soil it is, how much minerals it has, what kinds of minerals it has, and so on... Soil conditions are important.
Now that I have mentioned all of those, I will say "there is NO all-inclusive metal detector, that you can select, that will do everything for you, exactly like you would want it done". I just dashed all hope to the ground. But it is true! When you eat steak you select a fork and a knife as your tool. When you eat soup you select a soup spoon. When you stir the sugar in your coffee, you select the smaller teaspoon. Those are tools. A metal detector is a tool, a tool that has an ability to see an electromagnetic field... So depending on the task you have in mind, you select the proper metal detector tool for that job.
Then you have to understand that an bottle cap is a ferrous thing, as it belongs to the ferrous class, but can be separated from the aluminum class, which consists of thinner pieces of sheet aluminum, and those can be separated from the coin class, which are more thicker pieces of conductive metal. Then there is rusty iron. These have to all be taken into comparison with each other, and each is a different kind of conductive target, each affects each other and maskes each other, and each has a different resonate frequency...
In other words you shoud not compare apples with oranges, but only apples with apples, or much better compare Jonathan apples with only Jonathan apples, and then also, restrict the apples all to the same size for comparison...
So now I am going to agree with you. Frequency in KHz is just a number. But those numbers, what they are, what they do, are relevant to everything I mentioned above, to those cycles of frequency.
Now what was it you wanted to know? I seem to have been side tracked for some reason, and I have forgotten the question. So my final answer has to be, "yes and no" and "depending upon"!
I am still working on who came first, "the chicken or the egg"?
Melbeta
After all computers can do almost anything, with today's tech. 
I just can't stop thinking how it seems the technology is behind what it should be able do. 
