We have had the engineers at Olympia Express in Switzerland build us a custom digital manometer with a fitting that allows us to screw it directly to the top of the boiler.  If you have an Olympia espresso machine of any vintage and would be interested to have it calibrated to see how accurate the gauge on your machine is, then please get in touch.  We will also us this instrument to calibrate all the new Olympia machines we sell to UK customers.