cdm/src/main/java/ucar/nc2/dataset/conv/CF1Convention.java
public static String getZisPositive(String zaxisName, String vertCoordUnits) {
    if (vertCoordUnits == null) return CF.POSITIVE_UP;
    if (vertCoordUnits.isEmpty()) return CF.POSITIVE_UP;

    if (SimpleUnit.isCompatible("millibar", vertCoordUnits))
      return CF.POSITIVE_DOWN;

    if (SimpleUnit.isCompatible("m", vertCoordUnits))
      return CF.POSITIVE_UP;

    // dunno - make it up
    return CF.POSITIVE_UP;
  }
public static String getZisPositive(String zaxisName, String vertCoordUnits) {
    if (vertCoordUnits == null) return CF.POSITIVE_UP;
    if (vertCoordUnits.isEmpty()) return CF.POSITIVE_UP;

    if (SimpleUnit.isCompatible("millibar", vertCoordUnits))
      return CF.POSITIVE_DOWN;

    if (SimpleUnit.isCompatible("m", vertCoordUnits))
      return CF.POSITIVE_UP;

    // dunno - make it up
    return CF.POSITIVE_UP;
  }
Guess the value of ZisPositive based on z axis name and units

@param zaxisName      z coordinate axis name
@param vertCoordUnits z coordinate axis name
@return CF.POSITIVE_UP or CF.POSITIVE_DOWN