Multicollection (simultaneous) isotope ratio measurements were made with three different configurations: (1) three Si isotopes ( 28 Si -, Si -and 30 Si -) from silicon wafers (conductor) with ~1 pA Cs + and 4 x 4 µm 2 rasters measured on three EMs, (2) three Si isotopes from the same Si wafers with 600 pA Cs + and 10 x10 µm² rasters measured on three FCs, (3) oxygen isotopes ( 16 O -and 18 O -) from a polished Pt-coated quartz substrate (insulator) with 15 nA Cs + and 10 x10 µm² rasters measured on two FCs. The normal-incidence electron flood gun was used for charge compensation. The NanoSIMS-HR was tuned for >7000 MRP (10%-90% definition). Data were collected in multicollection "isotope mode" with 64 x 64 pixels. The duration of one analysis, including pre-analysis sputtering, automatic secondary ion beam focusing and centering, automatic mass line centering, and data acquisition, was 10 min, 2 min 30 sec, and 3 min, respectively. Multiple reproducibility tests were conducted, including tests with small (microns), medium (millimeters), and large (10s of millimeters) movements (Table ; see also Results). Magnet stability was maintained with NMR control.