How can you tell if the standard deviation you have got is big or small?

The degree of dispersion is called the Standard Deviation of your data if you take your Standard Deviation and divide it by the mean (you can then if asked multiply by 100 to have it in percentage). The Standard Deviation divided by the mean is called Coefficient of Variation. It is used to give a more general view of the Degree of Dispersion of the data (" Coefficient of Variation of 5%, or less, generally give us a feeling of good method performance").