Hi All
     I have constructed 3 long period seismographs which used info from STM's web site. They work well. What isn't working well is duplicating STM's equation results for the sensors response. I have tried my DOS version of mathcad and have just created the equations in Excel. I get the same results with both. However they differ from that  STM got and also Al Coleman. I have been able to duplicate most of their results except for the response slope at both ends of the velocity graph, especially at the low end. My graphs drop off too dramatically. Has anyone run the equations and duplicated STM's results with his seismograph characteristics? I am an engineer and understand equations. I suppose that I'm not reproducing some subtle portion of the equations, though I have stared at them for days. 
  Regards
  Barry