Hi Rob
Have tried out both of your above codes, the readings are still too high. I am wondering if it is still the reed switch although the electronic tacho uses this switch.
It seems to be ok up to about 2500RPM and then shoots up. I have tried out also on my workshop pillar dill which at max speed is 2800 and on this the arduino is ok, nice and steady between 2750 and 2850.
The shaft that I want to monitor is driven by a hydraulic motor and if I feather the oilflow to start with it starts and climes from o to 2500 ok but when the flow is full it shoots up but should be no more that 5000rpm max.
Here is the output from your first code
101, 7722
101, 8910
101, 8910
101, 7722
101, 8910
101, 7128
101, 10099
101, 10099
102, 10000
101, 10099
101, 12475
101, 10693
101, 10099
101, 8910
101, 10693
101, 8910
101, 10693
101, 8910
101, 8910
101, 7722
101, 8910
101, 10693
101, 10099
101, 12475
101, 10693
101, 12475
101, 10693
102, 12352
101, 11881
101, 11287
101, 11881
101, 10693
101, 10099
101, 10693
101, 10693
101, 12475
101, 11287
101, 12475
101, 10693
101, 13069
and the second
105, 11428
102, 11764
105, 11428
104, 11538
90, 13333
104, 11538
106, 11320
104, 11538
91, 13186
117, 10256
120, 10000
91, 13186
103, 11650
90, 13333
104, 11538
105, 11428
134, 8955
92, 13043
105, 11428
133, 9022
106, 11320
105, 11428
104, 11538
102, 11764
105, 11428
106, 11320
118, 10169
91, 13186
149, 8053
89, 13483
91, 13186
104, 11538
105, 11428
regards Tim