I have a Delta Plus running ISODAT NT. On occasion during a sequence, my middle cup, #4 (yes, it really is 4. Don't ask), will not acquire. 0 bkg, 0 peak height, 0 ratio, flat trace. The other two cups, #3 and #5 (masses 28 and 30, I do almost exclusively nitrogen only work) look just fine. I even get a 28/29 ratio trace, but no 29 signal. Next run everything is fine. This seems to have started when I switched to NT, but I had other more vexing problems with the Real32 version, so I'm inclined not to go back. Has anyone seen anything like this with either version? I'm going to defrag, cut down on the number of files in my acquisition directory and find a suitable sacrifice. Any other tips would be appreciated. Howard Howard Sanford 919-513-3039 North Carolina State University Dept. of Soil Science Box 7619 3114 Williams Hall Raleigh, NC 27695 http://www.soil.ncsu.edu/