About the frequency counter on the Hitachi scopes.
I have a 1585 and I'm frustrated by the frequency counter accuracy too. This model has a PEF-875 board and there's the uC and the frequency counter. I applied 1MHz from a Ublox GPS module and it reads 998.1KHz. If I touch one of the pins of X4101, the blue resonator in the picture, with an oscilloscope probe connected to a reasonably accurate frequency counter, the reading goes up to 999.6KHz and the frequency counter reads 12.006MHz. As you can see in the picture, there's a place for crystal oscillator but they decided to use a ceramic resonator. Really Hitachi? The PEF-875 board seems to have two 32 pins headers soldered to the one beneath so would be pretty hard to remove it and I may damage some pads. Again, really Hitachi?
I, being a bit of a precision nut, intend to desolder the resonator from the top and install a crystal that has much tighter tolerance and stability than a ceramic resonator. By my calculation, the crystal must have a load capacitance of 21.5pF so I don't need to change the two 33pF load capacitors shown in the schematic. A 20pF CL crystal should do it.
I'll let you know how it goes.