Hi Larry,
Picture a old lady with a set of knitting needles with leads attached to them, pressing the needles into different points of the PCB (pads, test points or component leads) and measuring resistance, inductance, waveforms etc between these points. Some machines may untilize 3 or 4 grannies.
All goes well until someone takes this lovely, clean surface mounted PCB and sprays some nasty toxic concoction on it (too much normally), and then doesn't heat it up long enough for this nasty chemical to evaporate off, before sending it over the molten river styx.
Now this once clean marvel of technology is covered in minging flux residue and the poor grandma can't push her needles through this crap to make a clean contact with the PCB.
Same for ICT, hence the development of flux buster pins.
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