user13605: 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?

user7508: 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().

13605: <p>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. </p>

<p>Possible choices are:</p>

<ol>
<li>Maximum double value</li>
<li>Minimum double value</li>
<li>NAN (I would also need a method to check is_nan as well)</li>
</ol>

<p>How can I accomplish this in the Arduino language?</p>
 7508: <p>This is a matter of personal preference. I like NAN because it is almost
always obvious it cannot be a valid value.</p>

<p>You can test for the value being NAN with
<a href="http://www.nongnu.org/avr-libc/user-manual/group__avr__math.html#ga468be9ed380771eca5a18e812b2470d4" rel="nofollow"><code>isnan()</code></a>.</p>
