Wireline logs are recorded on a cable after the bit is out of the hole. Logging-while-drilling tools make a similar record in the drill string, which is often the only log in a high-angle well, because a cable will not fall down a horizontal hole.
Depth on the log has to be tied to the driller's measured depth before the log is used to pick casing points or perforations. A curve is one measurement: gamma ray, resistivity, density, neutron. The log is the record. A saturation or a porosity written on a formation top is an interpretation of the log, not the log itself.