While reading about Minkowski's description of the fourth dimension time axis, I saw that by taking the product of the speed of light and time, he was able to give it a "spatial" geometric character of distance (i.e. light-years, light-seconds, or whatever). I then saw that he set c (the speed of light) to 1 in order to eliminate having to label the axis ct, giving it the label of just t for time. Since the speed of light (in a vacuum) is 300,000.000 m/s, how can a scientist or mathematician just decide to set it to a value of one? I am not a physicist nor a mathematician. I am just an aging 68 year old man that is curious and likes to learn new things. Can anyone (young or old) explain this to me? Thanks in advance.