Amps per Square Foot (ASF)
ASF is an early American unit for current density meaning Amps per Square Foot or Amp/foot2. This unit has largely been replaced by mA/cm2. To derive the conversion of ASF to mA/cm2 we simpy use unit analysis:
(929 cm2/foot2)/1000 mA/Amp= 0.929 (Amp/foot2) /(mA/cm2)=0.929 ASF/(mA/cm2)
Area Specific Resistance mV/100ASF to mOhm*cm2
Again mV/100ASF was an early American unit. This unit was used for measuring voltage losses due primarily due to membrane resistance. Really this is a resistance, but since the source of the losses were not always directly correlated with resistance it was very convenient to leave simply as a voltage loss. To derive the conversion of mV/100ASF to mOhm*cm2 we first divide mV by Amps to get mOhm*foot2:
1 mV/100ASF = 1 mV /(100 A/foot2) = 0.01 mOhm*foot2
Next we do some simple unit analysis:
1 mV/100ASF = 0.01 mOhm*foot2*(929 cm2/foot2)= 9.29 mOhm*cm2)
To end up with:
9.29 (mOhm*cm2)/(mV/100ASF)
Converting mOhm*cm2 to a Voltage Loss
To convert mOhm*cm2 to a voltage loss, multiply by the current density in Amp/cm2 to produce mV. For Example:
70 mOhm*cm2 * 1 Amp/cm2 = 70 mV
Caution
Today most people talk about losses in mOhm*cm2. Still, care should be made in assumptions about where these losses come from!