Why is the waveform response slow in 112Mpts and 10s/div modes?

When testing a 40KHz ultrasonic radar probe, when the ZDS2022 storage depth is adjusted to 112Mpts, the time base gear is set to 10s/div, the sampling rate is 500KSa/s, and when the pre-trigger is in the middle, it takes 1.5 minutes to see the waveform. Even if the horizontal arrow is adjusted to the far left, it takes 40 seconds to see the waveform. Why is this?

When the storage depth is set to 112Mpts, the time base is set to 10s/div, the sampling rate is 500KSa/s, and the total sampling time is 224s. At this time, the waveform time on the screen is only 10s/div*14div＝140s. In other words, there are 84s of waveform outside the screen, 42s on the left and 42s on the right. Therefore, when the pre-trigger is in the middle, you need to wait 112s (70s+42s=112s) to see the waveform; when the pre-trigger is adjusted to the left, you need to wait 42s.