These units measure emitted infrared; the laser is there to direct the
sensor. I use a unit with a 6:1 spot ratio (spot diameter is 1/6th of the
distance to the source) which is quite handy if you prepare shiny surfaces
with a spot of flat paint or tape. On the "prepared" surface of the timing
case of my Norton, my IR sensor read 15% low compared to an adjacent type K
thermocouple; close enough to be useful. Expect to pay 100 bucks for a
decent IR multimeter like ExTech.
Rick in Seattle
1960 TR3A
1970 BSA 441 Victor Special
1972 Norton 750 Commando Combat
1975 Norton 850 Commando Mk3
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