It is often the case that the Bison, EGG Geometrics, or whatever recording instrument does not contain enough information to complete the trace header. This is why paper observer's logs are filled out. Here is where the surveyor information is merged to complete the setting of trace headers. Header information like sample interval or number of samples are usually OK and included in the trace header when tools like bis2seg, egg2seg, topcon, topcon2, bhed, bnez, gensetg, setgeom, genref are run.