This reaction produces a Schiff base (R-N=CHR', R = beta chain, CHR'= glucose-derived), which is itself converted to 1-deoxyfructose. This second conversion is an example of an Amadori rearrangement. When blood glucose levels are high, glucose molecules attach to the hemoglobin in red blood cells. The longer hyperglycemia occurs in blood, the more glucose binds to hemoglobin in the red blood cells and the higher the glycated hemoglobin. Once a hemoglobin molecule is glycated, it remains that way. A buildup of glycated hemoglobin within the red cell, therefore, reflects the average level of glucose to which the cell has been exposed during its life-cycle. Measuring glycated hemoglobin assesses the effectiveness of therapy by monitoring long-term serum glucose regulation. A1c is a weighted average of blood glucose levels during the life of the red blood cells (117 days for men and 106 days in women). Therefore, glucose levels on days nearer to the test contribute substantially more to the level of A1c than the levels in days further from the test. This is also supported by data from clinical practice showing that HbA1c levels improved significantly after 20 days from start or intensification of glucose-lowering treatment. Several techniques are used to measure hemoglobin A1c. Laboratories use high-performance liquid chromatography (the HbA1c result is calculated as a ratio to total hemoglobin using an immunoassay; enzymatic assay; capillary electrophoresis; or boronate affinity chromatography. Point of care (e.g., doctor's office) devices use immunoassay ororonate affinity chromatography. In the United States, HbA1c testing laboratories are certified by the National Glycohemoglobin Standardization Program to standardize them against the results of the 1993 Diabetes Control and Complications Trial (DCCT). An additional percentage scale, Mono S has previously been in use by Sweden and KO500 is in use in Japan. The American Diabetes Association, European Association for the Study of Diabetes, and International Diabetes Federation have agreed that, in the future, HbA1c is to be reported in the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) units. IFCC reporting was introduced in Europe except for the UK in 2003; the UK carried out dual reporting from 1 June 2009  until 1 October 2011. Conversion between DCCT and IFCC is by the following equation:  Laboratory results may differ depending on the analytical technique, the age of the subject, and biological variation among individuals.