Centre of sample Collection Number of samples Mean of difference (‰) Standard deviation of difference (‰)
Physical Research Laboratory(PRL), Ahmedabad 253 1.1331 1.8308
National Institute of Hydrology(NIH), Roorkee 96 0.2604 2.8691
National Geophysical Research Institute(NGRI), Hyderabad 292 -1.0678 2.6194