diff --git a/pid/zone_interface.hpp b/pid/zone_interface.hpp
index f701064..a024c0e 100644
--- a/pid/zone_interface.hpp
+++ b/pid/zone_interface.hpp
@@ -7,18 +7,79 @@
 namespace pid_control
 {
 
+/**
+ * In a Zone you have a set of PIDs which feed each other.  Fan PIDs are fed set
+ * points from Thermal PIDs.
+ */
 class ZoneInterface
 {
   public:
     virtual ~ZoneInterface() = default;
 
-    virtual double getCachedValue(const std::string& name) = 0;
-    virtual void addSetPoint(double setpoint) = 0;
-    virtual void addRPMCeiling(double ceiling) = 0;
-    virtual double getMaxSetPointRequest() const = 0;
-    virtual bool getFailSafeMode() const = 0;
-    virtual double getFailSafePercent() const = 0;
+    /** If the zone implementation supports logging, initialize the log. */
+    virtual void initializeLog(void) = 0;
+    /** If the zone implementation supports logging, write string to log. */
+    virtual void writeLog(const std::string& value) = 0;
+
+    /** Return a pointer to the sensor specified by name. */
     virtual Sensor* getSensor(const std::string& name) = 0;
+
+    /* updateFanTelemetry() and updateSensors() both clear the failsafe state
+     * for a sensor if it's no longer in that state.
+     */
+    /** For each fan input in the zone, read each to update the cachedValue and
+     * check if the fan is beyond its timeout to trigger a failsafe condition.
+     */
+    virtual void updateFanTelemetry(void) = 0;
+    /** For each thermal input in the zone, read each to update the cachedValue
+     * and check if the sensor is beyond its timeout to trigger a failsafe
+     * condition.
+     */
+    virtual void updateSensors(void) = 0;
+    /** For each fan and thermal input in the zone, set the cachedValue to 0 and
+     * set the input as failsafe - to default the zone to failsafe before it
+     * starts processing values to control fans.
+     */
+    virtual void initializeCache(void) = 0;
+    /** Return cached value for sensor by name. */
+    virtual double getCachedValue(const std::string& name) = 0;
+
+    /** Add a set point value for the Max Set Point computation. */
+    virtual void addSetPoint(double setpoint) = 0;
+    /** Clear all set points specified via addSetPoint */
+    virtual void clearSetPoints(void) = 0;
+
+    /** Add maximum RPM value to drive fan pids. */
+    virtual void addRPMCeiling(double ceiling) = 0;
+    /** Clear any RPM value set with addRPMCeiling. */
+    virtual void clearRPMCeilings(void) = 0;
+
+    /** Compute the value returned by getMaxSetPointRequest - called from the
+     * looping mechanism before triggering any Fan PIDs. The value computed is
+     * used by each fan PID.
+     */
+    virtual void determineMaxSetPointRequest(void) = 0;
+    /** Given the set points added via addSetPoint, return the maximum value -
+     * called from the PID loop that uses that value to drive the fans.
+     */
+    virtual double getMaxSetPointRequest() const = 0;
+
+    /** Return if the zone has any sensors in fail safe mode. */
+    virtual bool getFailSafeMode() const = 0;
+    /** Return the rpm or pwm percent value to drive fan pids when zone is in
+     * fail safe.
+     */
+    virtual double getFailSafePercent() const = 0;
+
+    /** Return if the zone is set to manual mode.  false equates to automatic
+     * mode (the default).
+     */
+    virtual bool getManualMode(void) const = 0;
+
+    /** For each fan pid, do processing. */
+    virtual void processFans(void) = 0;
+    /** For each thermal pid, do processing. */
+    virtual void processThermals(void) = 0;
 };
 
 } // namespace pid_control