strange one: dashed line sometimes appears during an activity...maybe lasting for about 10-30 seconds?

sorry to pepper this forum, but here's something i have seen repeatedly and yet i need can pull out my phone (if i have it with me) to snap a picture. what i sometimes see momentarily is a dashed black line near the center of the screen. this appears on a four data field screen where this line runs horizontally through the two middle fields. is this a bug? a feature and indicative of "something."?

i hope this description is clear enough and i hope someone else knows what i'm talking about ;)