HI again, I am overwhelmed with good ideas! Thank you all so much. I will try do = deal with each. First of all the line voltage. I have not checked this, = however since the UPS showed the same problem, I don't think it is the = line voltage. I called the utility company and they said there were no = shifts related to capacitors at that time. They said there was a shift in = usage around that time but they couldn't be very specific. I'm pretty = sure its not a joke, our students are not that bright.... I thought about = streetlights but each is on its own photo cell and so they come on = irregularly. I did not have the seismograph running during the time = change so I don't know if it tracks. We are decidedly not in the desert = here in Minnesota so I doubt it is the building heating and cooling, = besides, this is too regular for something like that. =20 I like the idea put forward by Charles and Bob about AM radio interference.= I called around and there are two radio stations that have restricted = licences. One goes off the air at 8:45 and back on at 5:45. Very = interesting. The other station changes power level from 5000 to 1000 = watts at about that time. They couldn't be more specific. The station = that goes off air says that I could shield the coil with grounded aluminum = foil. So I took the box that I use as an air cover and taped aluminum = foil all over it. I attached a wire to it with electrical tape and = modified a regular AC 3-prong plug so that only the ground plug was there. = I attached the wire and plugged it into the power strip for the = computer. The trace that had been going more or less down the middle, = shifted to the left side of the screen. So it seems to be doing something.= Tonight I will watch the thing again, this time with the shield in place = and two radios going. If it happens again I'll see if it coincides with = the radio sign-off ( or signal decrease). Also , the radio station = changes its on-off times monthly so I can also see if it changes at the = end of the month. I am hopeful and will keep you all informed. Thanks = again for the help. John Tacinelli Earth Science Instructor Rochester Community and Technical College __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>