Effective range of overlap correction method tested by olivine-hosted melt inclusion. This was analyzed with an aperture of 20 × 20 μm and 1,024 scans. Open squares and solid diamonds are with and without the overlapping correction, respectively. Shaded line indicates ΔR/Rbaseline (=0.062) when the overlapping volume, y, is zero. The water content of the sample was 3.1 wt.% when the regression equation for basaltic composition (slope = 49.76) was applied. If the uncertainty in y is negligible, the uncertainty in ΔR of the overlap-corrected spectrum approximately becomes 1/(1 − y) times larger. The error values thus estimated were added to the overlapping-corrected data. In actuality, the uncertainty in ‘overlapping volume’ may not be negligible; therefore, the error value presented here is considered to be a minimum value.