Temporary Scribble line on Screen when Scrolling

[MacGromit]

I'm a newbie to this forum so hi to all.

Today I bought an Asus MemoPad ME173x and have just updated it from 4.2 to 4.4.2. Suddenly now when I scroll the screen I'm getting a temporary thin blue scribble line on the screen. When I scroll again this first line disappears but is replaced by the next scroll trail line.

Can anyone explain where this trail line is coming from please? I can't see any background drawing apps that might be causing it.

Many thanks for any help.

 

[MacGromit]

Sorry, I should also have said that I'm getting single x-y grid lines with a circle at the intersection.

 

[MacGromit]

I have found the solution to this issue. It is switched on and off via:

Settings > Developer options > Pointer location (Screen overlay showing current touch data).