For a normal distribution bell-shaped curve, one would have thought that the height should have an ideal value. Knowing this value may be one quick indicator to check if the data is normally distributed. 

However, I could not find its formal value. Most places, the shape is shown but not the y-axis measurements. http://www.stat.yale.edu/Courses/1997-98/101/normal.htm

In some graphs where it is mentioned, it is 0.4. http://en.wikipedia.org/wiki/File:Normal_Distribution_PDF.svg . But on the main page (http://en.wikipedia.org/wiki/Normal_distribution), value of 0.4 is not mentioned anywhere.

Is this the correct value and what is its mathematical basis? Thanks for your insight. 

Edit:

The three curves shown in @Glen_b 's answer and on the wiki page (with mean=0) have same mean but different SDs. All tests would show that no significant difference between them. But they are clearly from different populations. Which test can we then apply to determine the difference in standard deviations of two distributions?