Max double value or NAN as a sentinel value? I am in need of a sentinel value to use to assign to a double variable initially.
0 or -1 won't work because these values are valid values in my computation and I need a value that will stand out. 

Possible choices are:


Maximum double value
Minimum double value
NAN (I would also need a method to check is_nan as well)


How can I accomplish this in the Arduino language?
This is a matter of personal preference. I like NAN because it is almost
always obvious it cannot be a valid value.

You can test for the value being NAN with
isnan().