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Hello Rowland,
If I were you I would get a potentiometer (about 1K) and firstly try it in lieu
of a fixed resistor. 
I would be looking for the lowest resistance at which either instrument plays up
and similarly the highest reading and then use a fixed resistor of the mid way
value. 
BUT THEN ....... We are not in lockdown. 
If I WAS in lockdown, I would try the 220 ohm resistor and see how it goes.  It
certainly wont do any harm. 
Regards
Kingsley in Oz
Sent from my iPhone
> On 19 Jan 2021, at 7:29 pm, Rowland Carson <rowlandcarson@gmail.com> wrote:
> 
> 
> Im wiring my Europa XS with a 912ULS engine. I have fitted the 
> factory-supplied
UMA tacho and am also taking the engine tacho output to a MGL E-3 engine 
instrument
and a Smart Avionics CSC-1 prop controller.
> 
> The UMA manual calls for a 270 resistor across the engine tacho output (if the
readings are erratic). The MGL manual calls for 220 (and one is supplied).
> 
> With no electronics shops open nearby in lockdown, its going to be awkward 
> buying
a single 270 resistor. Does anyone know if using the 220 resistor Ive got
would make the UMA tacho unhappy? And conversely, would using a 270 make the
MGL instrument unhappy?
> 
> in friendship
> 
> Rowland
> 
> | Rowland Carson          ... that's Rowland with a 'w' ...
> | <rowlandcarson@gmail.com>            http://www.rowlandcarson.org.uk
> | Skype, Twitter: rowland_carson      Facebook: Rowland Carson
> 
> 
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