Bad Writing

The manual should have said:

"A crash or "unusual motion” of the vehicle can automatically trigger the camera’s recording function, [t]he recorder may not store more than 30 seconds of data before and after the event that triggers its recording function. [B]ut the driver can also manually operate it for the purpose of monitoring his driving performance. "

Even with this revision, "the event" was not defined earlier, we can only guess event = crash/unusual motion because they share the word "trigger".

I hate bad writing. This text is written by an engineer, not an English major.