This is merely my own opinion after having thought about this for ages-Nearly everything that Chiropractors say about what they are doing, how, or why is baseless.
Chiropractors use three methods to find spinal misalignments:
Palpation- Feeling the spine and moving the joints. This has been shown conclusively by studies not to be effective and has no interexaminer reliability.
Intrumentation- The most common being heat sensing equipment or EEG equipment that measures and graphs heat and electrical activity of the paraspinal muscles, looking for imbalances. Chiropractors market this as a perfect science. I actually worked in an office that used this. All 3 of the Chiropractors working there agreed that it was perfectly worthless. But we charged for it, and we rationalized it all by saying that it is "good for patient education". Every Chiropractic friend I have agrees that these machines with names like "subluxation station" or "myovisions" are perfectly worthless. The studies on them are pointless and fruitless. They provide no value at all to the practitioner. The value is merely in giving the patient an artificial visual aid to show them that their body is assymetrical, and to lead them to the false assumption that this is pathological and Chiropractic care is going to improve their lives by fixing this. One practicing friend I have is irate that Palmer College (where we went to school) has incorporated these junk machines in their student clinics.
X-rays- One of the most common strategems Chiropractors are trained to use is to show a "normal" spine in comparison with an x-ray of the patient's slightly crooked spine and then claim that we can help you make this better. False. Almost nobody has a straight spine, and no amount of adjusting is going to make an adult spine straight. To make matters worse, the chiropractor telling you this knows it! It's just more "patient education". Needless to say, the x-ray analysis has been shown in studies done by Chiropractors to have a worthless degree of interexaminer reliability. Reading x-rays for pathology such as disc herniations, degeneration, fractures etc... is a different issue and is not what I'm discussing here.
When taken as individual things- X-rays, Instrumentation, and Palpation have been shown in research done by Chiropractors to be virtually worthless at informing the Chiropractor what to adjust. But Chiropractors maintain that if you combine all three worthless detection systems together, they make a good system of detection.
Since most of the Chiropractors I know are intelligent enough not to "give a shit about subluxations" anyways, it doesn't much matter. "Being a subluxation fixer is like being a deaf piano tuner", I heard one person say.