Handling double (8 byte) in Arduino mega 2560?
In the Arduino there is no such thing as a double. A double is just another name for a float.

So you will have to either:


Manually interpret the double format data and calculate that into a float value, or
Send the value as some other format, such as float (32-bit), ASCII text, or (a selection of) integer values.


Since you can't actually use anything more than float, sending data with a higher resolution is pointless, so you are probably best off just sending it as a float.