diff --git a/pid/zone_interface.hpp b/pid/zone_interface.hpp
index 982e051..7d59497 100644
--- a/pid/zone_interface.hpp
+++ b/pid/zone_interface.hpp
@@ -42,8 +42,23 @@
      */
     virtual void initializeCache(void) = 0;
 
+    /** Optionally adds fan outputs to an output cache, which is different
+     * from the input cache accessed by getCachedValue(), so it is possible
+     * to have entries with the same name in both the output cache and
+     * the input cache. The output cache is used for logging, to show
+     * the PWM values determined by the PID loop, next to the resulting RPM.
+     */
+    virtual void setOutputCache(std::string_view name,
+                                const ValueCacheEntry& values) = 0;
+
     /** Return cached value for sensor by name. */
     virtual double getCachedValue(const std::string& name) = 0;
+    /** Return cached values, both scaled and original unscaled values,
+     * for sensor by name. Subclasses can add trivial return {value, value},
+     * for subclasses that only implement getCachedValue() and do not care
+     * about maintaining the distinction between scaled and unscaled values.
+     */
+    virtual ValueCacheEntry getCachedValues(const std::string& name) = 0;
 
     /** Add a set point value for the Max Set Point computation. */
     virtual void addSetPoint(double setpoint, const std::string& name) = 0;