percentage relative error, er(%) 

https://doi.org/10.1351/goldbook.P04486
The relative error expressed in percent. It can be calculated from the relative error by multiplying by 100. Comment: The term 'percentage relative error' should always be quoted in full, rather than 'error' or 'percentage error' to avoid confusion.
Source:
PAC, 1994, 66, 595. (Nomenclature for the presentation of results of chemical analysis (IUPAC Recommendations 1994)) on page 601 [Terms] [Paper]