And since the development of most radiometric dating methods used each other to verify their own development,
Could you elaborate on this? I believe this to be an assertion made from ignorance of what has actually gone on.
Your ruler analogy is a start but it is not a good representation of the actual case with dating methods.
A better analogy is is I measure a distance across a room with a ruler that is marked as being 12 inches from the manufacturer, a rolled tape measure that is marked in meters from a different manufacturer, a laser interferometer set up to measure distance, a sonar device to measure distance and got close agreement with all 4 methods. If someone then suggested that the room was not 54 feet across (within errors in measurements) they would have to explain how all 4 methods happened to agree.
In addition, for some of the methods I can more directly measure the length. For example, my shoes happen to be almost exactly a foot long and if the ruler is the same length I can take it as being close to right.
Try again.