I've noticed that the X axis on my TDS5000 series oscilloscope is occasionally truncated to only 8 divisions...what's wrong?

I've noticed that the X axis on my TDS5000 series oscilloscope is occasionally truncated to only 8 divisions...what's wrong?

Long acquisition durations at high sample rates can result in truncated (X-axis) displays, for example:

Under optimal settings, an acquisition taken at 40mS/div will have a duration of 400mS, (i.e. 40mS/div X 10 div = 400mS).

If however, the resolution is @ 40nS/pt (40^ -9) and RL is @ 8M (8^ 6), the acquisition duration will be [(40^ -9) X (8^ 6)] = 320mS.

At 40mS/div, the duration will show up as a truncated X-axis display of only 8 div, (i.e. 400mS/div X 8div = 320mS).

Long duration acquisitions at high sample rates can result in truncated X-axis displays. Don't be concerned though, the scope is smart enough to figure it out for you and provide a correct display...trust the scope