7704A - Sweep speed changes near center of trace


So, after getting a trace from the function generator, I'm noticing that the sweep speed changes somewhere near the mid-point and the trace from the mid-point to the right edge is slightly faster than the first half. For example, if I display two cycles from the left side to the center, there are only 1-3/4 cycles on the right side of the screen (I hope that's a clear explanation of what I'm seeing).

This is occurring with three different time bases so I presume the problem is in the display unit. Anyone know where I might find the problem? Horizontal amplifier?

Also I presume this is not normal and isn't an operator error.

Barry - N4BUQ