It sounds like you were checking for variations in height from the spindle or head to the table along the entire X and Y axes travel by moving the table? If so, that is a good test, but not necessarily tramming. Another issue is that if the indicator is attached to the spindle or head, and the table traversed, you could have a situation where as the table travels, it sags towards the overhanging end, but you would not necessarily find the discrepancy at the indicator. You can produce a convex part that indicates perfectly to the head. That is a common problem with milling machines and surface grinders -- an even and significant curve in the table travel caused by table overhang wear or looseness makes little or no movement of the indicator. If the mill is new or nearly new, it may not have that issue, depending... My old surface grinder has that issue, to a minor extent, for sure.