For a good quality mesh, skweness, aspect ratio, and the size change value should be under limit. Aspect ratio and the skewness represent the quality of a single cell, where as the size change represents the ratio of the size of a cell to its neighboring cell.
Size change > 0 .
Aspect Ratio >1
For good quality mesh, the skewness must be less than 0.85 (<0.9 is average, >0.95 is poor). There is no limit for the aspect ratio and the size range. However, it is better to limit these two <10. Depending on the problem, region of interest, accuracy of the solution, etc, the limit varies.
Skewness is defined as the difference between the shape of the cell and the shape of an equilateral cell of equivalent volume.
The Size Change specification represents the maximum ratio of the area (for 2-D elements) or volume (for 3-D elements) of an element rela¬tive to its neighboring elements. To calculate the Size Change value for any ele¬ment i, GAMBIT first computes the individual ratios of its area or volume relative to each of its neighboring elements.
By definition, size change > 0 . Size change value 1 represents an element that is surrounded by elements the areas or volumes of which are exactly equal to its own.
The "aspect ratio" is a measure of the stretching of a cell, and is defined as the ratio of the maximum distance between the cell centroid and face centroids to the minimum distance between the nodes of the cell