Hi Martyn, you may be able to use a Wavecrest DTS-2070 or better DTS-2075 Time Interval Analyzer for this. It has up to 40K samples/second capture capability, with +/-25ps single-shot accuracy, <<10ps RMS noise, and 800 Femtoseconds resolution. If you can capture the data via GPIB, you should be able to calculate better than 1E-012 per second with the massive over-sampling the unit can do. See: _http://www.wavecrest.com/technical/pdf/2079003A.pdf_ (http://www.wavecrest.com/technical/pdf/2079003A.pdf) These used to cost $60K+, now you can get them for $500 on Ebay. bye, Said In a message dated 5/7/2008 09:53:29 Pacific Daylight Time, martyn@ptsyst.com writes: I really need to measure 10 MHz to an accuracy of 1 part in 10E-13 / second (ignoring the accuracy of my workshop standard). I've tried multiplying the 10 MHz to the GHz frequencies, but never manage to improve on the technique I mention in my first question. Any ideas for a relatively cheap way of doing this. I actually represent a company that can measure to parts in 10E-15 in one second, but their boxes costs $50k. Best Regards Martyn **************Wondering what's for Dinner Tonight? Get new twists on family favorites at AOL Food. (http://food.aol.com/dinner-tonight?NCID=aolfod00030000000001)