diff --git a/hes-engine/src/diff.rs b/hes-engine/src/diff.rs
index 6830d66d..1e46b0c3 100644
--- a/hes-engine/src/diff.rs
+++ b/hes-engine/src/diff.rs
@@ -170,6 +170,17 @@ impl Diff for State {
                 .short_units()
                 .diff(&other.resources.available.short_units()),
         ));
+        changes.push(Change::Nested(
+            "resource_surplus".into(),
+            (self.resources.available
+                - self.resource_demand.total())
+            .short_units()
+            .diff(
+                &(other.resources.available
+                    - other.resource_demand.total())
+                .short_units(),
+            ),
+        ));
         changes.push(Change::Nested(
             "feedstocks".into(),
             self.feedstocks.available.short_units().diff(
diff --git a/hes-engine/src/events/effects.rs b/hes-engine/src/events/effects.rs
index c309df5e..fb1052c7 100644
--- a/hes-engine/src/events/effects.rs
+++ b/hes-engine/src/events/effects.rs
@@ -530,7 +530,14 @@ impl Effect {
                 state.output_demand.modifier[*output] += amount;
             }
             Effect::Output(output, pct_change) => {
-                state.produced.factor[*output] += pct_change;
+                for process in state
+                    .world
+                    .processes
+                    .iter_mut()
+                    .filter(|p| p.output == *output)
+                {
+                    process.output_modifier += pct_change;
+                }
             }
             Effect::OutputForFeature(feat, pct_change) => {
                 for process in state
@@ -857,7 +864,14 @@ impl Effect {
                 state.output_demand.modifier[*output] -= amount;
             }
             Effect::Output(output, pct_change) => {
-                state.produced.factor[*output] -= pct_change;
+                for process in state
+                    .world
+                    .processes
+                    .iter_mut()
+                    .filter(|p| p.output == *output)
+                {
+                    process.output_modifier -= pct_change;
+                }
             }
             Effect::OutputForFeature(feat, pct_change) => {
                 for process in state
@@ -1200,4 +1214,17 @@ mod tests {
         state.world.update_climate(temp_prev);
         assert_eq!(state.world.temperature, temp_next);
     }
+
+    #[test]
+    fn test_output_demand_amount() {
+        let mut state = State::default();
+        state.output_demand.base.plant_calories = 5.;
+        let effect =
+            Effect::DemandAmount(Output::PlantCalories, 1.);
+        state.apply_effects(&[effect], None);
+        assert_eq!(
+            state.output_demand.of(Output::PlantCalories),
+            6.
+        );
+    }
 }
diff --git a/hes-engine/src/state.rs b/hes-engine/src/state.rs
index 3ec1f073..62656882 100644
--- a/hes-engine/src/state.rs
+++ b/hes-engine/src/state.rs
@@ -797,14 +797,12 @@ impl State {
 
 #[derive(Serialize, Deserialize, Clone, PartialEq)]
 pub struct Production {
-    pub factor: OutputMap,
     pub amount: OutputMap,
     pub by_process: BTreeMap<Id, f32>,
 }
 impl Default for Production {
     fn default() -> Self {
         Self {
-            factor: OutputMap::splat(1.),
             amount: OutputMap::default(),
             by_process: BTreeMap::default(),
         }
@@ -812,11 +810,11 @@ impl Default for Production {
 }
 impl Production {
     pub fn of(&self, output: Output) -> f32 {
-        self.amount[output] * self.factor[output]
+        self.amount[output]
     }
 
     pub fn total(&self) -> OutputMap {
-        self.amount * self.factor
+        self.amount
     }
 }