The double tick indicates that the phone has received the message, but it doesn't mean that it has been read.
however, on an iphone, the message can come through to the lock screen, which could mean that the receiver has read a snip of the message. It is only when the phone has been unlocked that it will be doubled ticked.
difference between single layer and double winding
screw thread are single threads which means they are not double
No
in programming, single quotes are for characters, and double quotes are for string, but in php, javascript, html, css i don't see any difference between the two.
the difference is that DNA is a double helix and RNA is a single chain
single destroys the brain and double destroys the spinal cord or central nervous system
A twin bedroom has two single beds, a double bedroom has a double bed!
There isn't an immediate difference in comfort between a single and double pillow top, but you are able to flip double pillow top mattresses. This can make it more comfortable in the long run and may help it last longer. Double pillow tops do tend to be more expensive than single ones.
clarinet is a single reed instrument and the oboe is a double reed, that is really the only difference
One cutting edge vs two
See Related Links below
A single vent is down the middle A double vent has a vent near the sides