I’ve not been able to get a decent match between my spectra & the Miles references of the group of stars in Taurus reported by Robin in “Testing ALPY 600”. I wavelength calibrated HD27819 using ISIS Pre-defined Mode [Balmer Lines] giving an RMS error of approx. 0.3A and then calculated the instrument response. The corrected spectrum of HD27819 matched well with it’s Miles reference. However, when I used this to calibrate the other spectra the comparisons with their Miles references are significantly in error [see fig]. There is clearly something amiss in my set-up or measurements or reduction method, but I haven’t been able to determine what. I’ve repeated the process using HD27962 with the same outcome – RMS errors in this instance of approx. 0.15A, good match of corrected spectrum with it’s Miles reference, but significant errors in other spectra when it’s used for calibration. The instrument responses calculated using HD27819 & HD27962 are markedly different. Am using Celestron C6 SCT @ f/10 with ATIK 314l+ & ALPY w/o calibration module. Wondered if it might be mismatch in focal ratio with ALPY or if not might others have some suggestions w.r.t. where I might be going wrong?