The likelihood is the product of the heights of all the green connections from the sample points to the gaussian curve.
The posted value is the ratio of the current likelihood to the largest possible likelihood.
To fit the candidate normal distribution to the sample :
* Translate it by translating the top of the curve with your mouse,
* Change its width (standard deviation) by translating either side of the curve with your mouse.
Fine-tune the position and width of the curve by clicking and keeping your mouse button down :
* Above the top of the curve to make it taller (and therefore narrower),
* In the area below the curve to make it shorter (and therefore wider),
* On either side of the curve to translate it.