The age "rounding" applies only to the 1841 census and only to ages 15 and over, and even then it was not universally applied.

It is wise to treat all census ages and birth places only as indications. They are useful for confirming data from other sources but are not very good as primary evidence.

The entries in the census books were copied from other forms and are thus subject to copying errors.

The original forms (which were destroyed after copying and so are not available) were also liable to errors depending on who provided the information.