Perhaps a related matter is this statement at the bottom of page 66 of the User's Guide ->
"In the horizontal direction, the screen can display a maximum of 700 points with the leftmost as 350 and the rightmost as -350."
Left is negative number and right is positive number. This would indicate the age of the data point rather than the time of occurrence as is usual. Maybe the firmware writer got it right in his own mind, just different to the rest of the world.