When people refer to ppm are they referring to 500 or 700 conversion?

[nocreativity]

when people refer to ppm are they referring to the 500 or 700 conversion? I guess what is the general standard ---

 

[zolar]

ppm meters measure electroconductivity [volts, amps,watts]

this number is multiplied by a conversion factor to get parts per million the two conversion factors relate to differing standards

like[miles vs kilometers]

some MJ forum boards in europe have threads that give the math and tell how to get the units to agree in more detail

the thing to remember is that two ppm numbers as a target

may have a signifigant real difference in percentage of nutrients
even if both are saying 1111 ppm because of the conversion factor difference