Help me decipher 'Chinglish' LED DC meter product description

[nzo]

I have a silly question involving the 'Chinglish' product description for a couple of Mini Red LED DC 0-99.9V Digital Panel Voltmeters I purchased off of Ebay.

This is the link to the product.

The seller writes:

1 - "Supply Power: 5V or 6-15V Optional"

and a bit further down:

2 - "We can Power the meter by the same source being measured (Common Ground)."

After reading this I assumed that I could just connect this meter to the source being measured (0-99.9v) and the meter would display the result. I also assumed that this meter, unlike many of the others available, did not need a separate DC supply for the whole thing to work, since it said "5V or 6-15V Optional".
Note: For some reason my Firefox does not show the wiring diagrams.Am I correct in thinking that this meter does need a separate DC supply? If it does, what's the point of having a common ground? Many thanks!

For some reason the forum software is munging my post formatting

[ElektroQuark]

Part 1:

I understand that your panel has to be powered with 5V, or 6-15V if you have chosen the second option for the device.

Part 2:

You don't need a floating (from the device under test) power supply for the panel, you can use one that uses the same ground that your DUT. You can't power it with 80V for example.

[nzo]

EdoNork...OK, got it. Thank you!