Measurement value from good condition mobilephone board sometime needed to do analyze to the board that have some problem, mobilephone technician usually do measurement to easiest pads that they cant found in the boards, for example when you do analyze problem on the lcd symtomps, you will do measurement to the lcd socket or connector in the mainboard, to check this board first thing you wanna do is looking for possibility one or more of their line is broken and not connected to their circuit, this is why you will do resistance level measurement, as we know all of closed circuit will have resistance from their load, we can do this by measure the resistance between all pads of this socket and the ground pads.
In the old school ways, we can use analog multimeter and select to ohm meter, and put the black probe to the ground pad and then red probe to pads that we want to measure, and will show to us the possibility of broken line when the resistance level shown is too high, and multimeter needle itsnt move at all, no matter we adjust selector to x1, x10, x100, x1K, its still not move, and said as infinite resistace. the other possibilites is that line will shown ( 0 ) zero ohm to the ground, which is we can say this pads have short circuit and connected to ground, both of this condition cant acceptable to the pads that have their pads to some circuit, cant be infinite and cant be zero resistance to ground.
Now days, mobilephone technician use digital multimeter, and will not select ohm meter that will need more time to show persist resistance level, mobilephone technician more comfortable use dioda test mode to do the similiar things, btw two kind of test have similiar protocol to works, that one of probe will have voltage and the other probe will recieve voltage, when we put one of probe in some circuit line that have active component inside, it will be have forward bias and reverse bias, so... if some multimeter provide 3 volt in red probe, its value will be cut off the value depend it reserve bias and forward bias, and when this voltage recieved by black probe this voltage will be lower than 3 volt right, it will make mobilephone technician analyze the circuit is ok, not just it still connected but the load and the active component still cut the voltage, how much the voltage need displayed after cut off from normal circuit ? you need to measure to normal pcb, in the pragmafix we do this for you, and you can use it as gudance for youre measurement, bassicly not all of mobilephone boards need precision value use dioda test mode, you oftenly need only analog multimeter use ohm meter to check broken line or short to ground possibilty, only mobilephone that have many circuit in pararel active component / ic need precision value use dioda test mode, for example Apple devices, you need to know some of pads still connected to A ic or B ic use the value of dioda test mode.