Dear Colleagues. We had to purchase a new carbon coater around a year ago, as our trusty old Emitech K950x gave up. The new coater is from Agar (Agar Auto Carbon Coater), and we’re really struggling to control the thickness of the carbon coating and get substantial variations between runs. We thought it might be a clever idea to use the C-Ka signal measured on our LDE2H crystal to create a general calibration curve for individual sections, but what appeared to be a simple idea, doesn’t seem to quite work. There are obviously some matrix effects, and after testing the method on glass, I resorted to making calibration curves on plagioclase, augite and ilmenite (fig. 1). The curves look okay, but when I read off the signals and add a manual thickness estimate in the ‘Analyze’ ‘calculation options’, then the software seems to vastly over-correct. Has anybody had success with a similar idea, or might in any other way share insight into what I may be doing wrong?