Based upon your statement that the 260 is matched to the TS-58 sender then full current would be 260 degrees, so if you have a 230 gauge where full current indicates 230 (when at the sender it is 260) then the 230 gauge is indicating 30 degrees low at full deflection.
The 260 gauge range is 90-260, not sure what the 230 gauge is, but assuming both gauges start at 90 then the 230 gauge will be off by the following;
Actual T = (Indicated T - 90)*0.214 + Indicated T
Julian
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