diff --git a/src/app/components/InternalSlot.jsx b/src/app/components/InternalSlot.jsx
index 84e12a8a..fb81b260 100644
--- a/src/app/components/InternalSlot.jsx
+++ b/src/app/components/InternalSlot.jsx
@@ -49,7 +49,7 @@ export default class InternalSlot extends Slot {
           { m.rangeLS ? <div className={'l'}>{translate('range')}: {m.rangeLS}{u.Ls}</div> : null }
           { m.rangeLS === null ? <div className={'l'}>∞{u.Ls}</div> : null }
           { m.rangeRating ? <div className={'l'}>{translate('range')}: {m.rangeRating}</div> : null }
-          { m.getHullReinforcement() ? <div className={'l'}>+{formats.int(m.getHullReinforcement() + ship.baseArmour * m.getModValue('hullboost'))} <u className='cap'>{translate('armour')}</u></div> : null }
+          { m.getHullReinforcement() ? <div className={'l'}>+{formats.int(m.getHullReinforcement() + ship.baseArmour * m.getModValue('hullboost') / 10000)} <u className='cap'>{translate('armour')}</u></div> : null }
           { m.passengers ? <div className={'l'}>{translate('passengers')}: {m.passengers}</div> : null }
 	  { m && validMods.length > 0 ? <div className='r' ><button onClick={this._toggleModifications.bind(this)} onContextMenu={stopCtxPropagation} onMouseOver={termtip.bind(null, 'modifications')} onMouseOut={tooltip.bind(null, null)}><ListModifications /></button></div> : null }
 
diff --git a/src/app/components/Modification.jsx b/src/app/components/Modification.jsx
index c73d0607..f9a74df4 100644
--- a/src/app/components/Modification.jsx
+++ b/src/app/components/Modification.jsx
@@ -24,7 +24,7 @@ export default class ModificationsMenu extends TranslatedComponent {
   constructor(props, context) {
     super(props);
     this.state = {};
-    this.state.value = this.props.m.getModValue(this.props.name) * 100 || 0;
+    this.state.value = this.props.m.getModValue(this.props.name) / 100 || 0;
   }
 
   /**
@@ -32,14 +32,14 @@ export default class ModificationsMenu extends TranslatedComponent {
    * @param {Number} value The value to set
    */
   _updateValue(value) {
-    let scaledValue = Math.floor(Number(value) * 100) / 10000;
+    let scaledValue = Math.floor(Number(value) * 100);
     // Limit to +1000% / -100%
-    if (scaledValue > 10) {
-      scaledValue = 10;
+    if (scaledValue > 10000) {
+      scaledValue = 10000;
       value = 1000;
     }
-    if (scaledValue < -1) {
-      scaledValue = -1;
+    if (scaledValue < -1000) {
+      scaledValue = -1000;
       value = -100;
     }
     let m = this.props.m;
diff --git a/src/app/shipyard/Module.js b/src/app/shipyard/Module.js
index cb1a5d25..8eb3befc 100755
--- a/src/app/shipyard/Module.js
+++ b/src/app/shipyard/Module.js
@@ -28,16 +28,16 @@ export default class Module {
   /**
    * Get a value for a given modification
    * @param {Number} name  The name of the modification
-   * @return {Number}      The value of the modification, as a decimal value where 1 is 100%
+   * @return {Number}      The value of the modification, as an integer value scaled so that 1.23% == 123
    */
   getModValue(name) {
-    return this.mods  && this.mods[name] ? this.mods[name] / 10000 : null;
+    return this.mods  && this.mods[name] ? this.mods[name] : null;
   }
 
   /**
    * Set a value for a given modification ID
    * @param {Number} name   The name of the modification
-   * @param {Number} value  The value of the modification, as a decimal value where 1 is 100%
+   * @param {Number} value  The value of the modification, as an integer scaled so that -2.34% == -234
    */
   setModValue(name, value) {
     if (!this.mods) {
@@ -47,8 +47,8 @@ export default class Module {
     if (value == null || value == 0) {
       delete this.mods[name];
     } else {
-      // Store value with 2dp
-      this.mods[name] = Math.round(value * 10000);
+      // Round just to be sure
+      this.mods[name] = Math.round(value);
     }
   }
 
@@ -61,7 +61,7 @@ export default class Module {
   _getModifiedValue(name, additive) {
     let result = this[name] || (additive ? 0 : null); // Additive NULL === 0
     if (result != null) {
-      const modValue = this.getModValue(name);
+      const modValue = this.getModValue(name) / 10000;
       if (modValue) {
         if (additive) {
           result = result + modValue;
@@ -299,7 +299,7 @@ export default class Module {
     if (this['minmass']) {
       result = this['minmass'];
       if (result) {
-        let mult = this.getModValue('optmass');
+        let mult = this.getModValue('optmass') / 10000;
         if (mult) { result = result * (1 + mult); }
       }
     }
@@ -324,7 +324,7 @@ export default class Module {
     if (this['maxmass']) {
       result = this['maxmass'];
       if (result) {
-        let mult = this.getModValue('optmass');
+        let mult = this.getModValue('optmass') / 10000;
         if (mult) { result = result * (1 + mult); }
       }
     }
@@ -341,7 +341,7 @@ export default class Module {
     if (this['minmul']) {
       result = this['minmul'];
       if (result) {
-        let mult = this.getModValue('optmul');
+        let mult = this.getModValue('optmul') / 10000;
         if (mult) { result = result * (1 + mult); }
       }
     }
@@ -366,7 +366,7 @@ export default class Module {
     if (this['maxmul']) {
       result = this['maxmul'];
       if (result) {
-        let mult = this.getModValue('optmul');
+        let mult = this.getModValue('optmul') / 10000;
         if (mult) { result = result * (1 + mult); }
       }
     }
diff --git a/src/app/shipyard/Ship.js b/src/app/shipyard/Ship.js
index 0de12dec..11b5db17 100755
--- a/src/app/shipyard/Ship.js
+++ b/src/app/shipyard/Ship.js
@@ -195,7 +195,7 @@ export default class Ship {
     if (this.shield > 0) {
       const sgSlot = this.findInternalByGroup('sg');
       if (sgSlot != null) {
-        let brokenRegenRate = 1 + sgSlot.m.getModValue('brokenregen');
+        let brokenRegenRate = 1 + sgSlot.m.getModValue('brokenregen') / 10000;
         // 50% of shield strength / recovery recharge rate + 15 second delay before recharge starts
         return ((this.shield / 2) / (sgSlot.m.recover * brokenRegenRate)) + 15;
       }
@@ -213,7 +213,7 @@ export default class Ship {
     if (this.shield > 0) {
       const sgSlot = this.findInternalByGroup('sg');
       if (sgSlot != null) {
-        let regenRate = 1 + sgSlot.m.getModValue('regen');
+        let regenRate = 1 + sgSlot.m.getModValue('regen') / 10000;
         // 50% -> 100% recharge time, Bi-Weave shields charge at 1.8 MJ/s
         return (this.shield / 2) / ((sgSlot.m.grp == 'bsg' ? 1.8 : 1) * regenRate);
       }
@@ -399,7 +399,7 @@ export default class Ship {
    * Set a modification value
    * @param {Object} m The module to change
    * @param {Object} name The name of the modification to change
-   * @param {Number} value The new value of the modification
+   * @param {Number} value The new value of the modification.  The value of the modification is scaled to provide two decimal places of precision in an integer.  For example 1.23% is stored as 123
    */
   setModification(m, name, value) {
     // Handle special cases
@@ -1136,7 +1136,7 @@ export default class Ship {
       if (slot.m && slot.m.grp == 'hr') {
         armour += slot.m.getHullReinforcement();
         // Hull boost for HRPs is applied against the ship's base armour
-        armour += this.baseArmour * slot.m.getModValue('hullboost');
+        armour += this.baseArmour * slot.m.getModValue('hullboost') / 10000;
 
         hullExplRes *= (1 - slot.m.getExplosiveResistance());
         hullKinRes *= (1 - slot.m.getKineticResistance());
@@ -1220,7 +1220,7 @@ export default class Ship {
     let bulkheadMods = new Array();
     if (this.bulkheads.m && this.bulkheads.m.mods) {
       for (let modKey in this.bulkheads.m.mods) {
-        bulkheadMods.push(Modifications.modifiers.indexOf(modKey) + ':' + Math.round(this.bulkheads.m.getModValue(modKey) * 10000));
+        bulkheadMods.push(Modifications.modifiers.indexOf(modKey) + ':' + this.bulkheads.m.getModValue(modKey));
       }
     }
     allMods.push(bulkheadMods.join(';'));
@@ -1229,7 +1229,7 @@ export default class Ship {
       let slotMods = new Array();
       if (slot.m && slot.m.mods) {
         for (let modKey in slot.m.mods) {
-          slotMods.push(Modifications.modifiers.indexOf(modKey) + ':' + Math.round(slot.m.getModValue(modKey) * 10000));
+          slotMods.push(Modifications.modifiers.indexOf(modKey) + ':' + slot.m.getModValue(modKey));
         }
       }
       allMods.push(slotMods.join(';'));
@@ -1238,7 +1238,7 @@ export default class Ship {
       let slotMods = new Array();
       if (slot.m && slot.m.mods) {
         for (let modKey in slot.m.mods) {
-          slotMods.push(Modifications.modifiers.indexOf(modKey) + ':' + Math.round(slot.m.getModValue(modKey) * 10000));
+          slotMods.push(Modifications.modifiers.indexOf(modKey) + ':' + slot.m.getModValue(modKey));
         }
       }
       allMods.push(slotMods.join(';'));
@@ -1247,7 +1247,7 @@ export default class Ship {
       let slotMods = new Array();
       if (slot.m && slot.m.mods) {
         for (let modKey in slot.m.mods) {
-          slotMods.push(Modifications.modifiers.indexOf(modKey) + ':' + Math.round(slot.m.getModValue(modKey) * 10000));
+          slotMods.push(Modifications.modifiers.indexOf(modKey) + ':' + slot.m.getModValue(modKey));
         }
       }
       allMods.push(slotMods.join(';'));
@@ -1295,7 +1295,10 @@ export default class Ship {
     let bulkheadMods = new Array();
     if (this.bulkheads.m && this.bulkheads.m.mods) {
       for (let modKey in this.bulkheads.m.mods) {
-        bulkheadMods.push({ id: Modifications.modifiers.indexOf(modKey), value: Math.round(this.bulkheads.m.getModValue(modKey) * 10000) });
+        // Filter out invalid modifications
+        if (Modifications.validity['bh'] && Modifications.validity['bh'].indexOf(modKey) != -1) {
+          bulkheadMods.push({ id: Modifications.modifiers.indexOf(modKey), value: this.bulkheads.m.getModValue(modKey) });
+        }
       }
     }
     slots.push(bulkheadMods);
@@ -1304,7 +1307,10 @@ export default class Ship {
       let slotMods = new Array();
       if (slot.m && slot.m.mods) {
         for (let modKey in slot.m.mods) {
-          slotMods.push({ id: Modifications.modifiers.indexOf(modKey), value: Math.round(slot.m.getModValue(modKey) * 10000) });
+          // Filter out invalid modifications
+          if (Modifications.validity[slot.m.grp] && Modifications.validity[slot.m.grp].indexOf(modKey) != -1) {
+            slotMods.push({ id: Modifications.modifiers.indexOf(modKey), value: slot.m.getModValue(modKey) });
+          }
         }
       }
       slots.push(slotMods);
@@ -1314,7 +1320,10 @@ export default class Ship {
       let slotMods = new Array();
       if (slot.m && slot.m.mods) {
         for (let modKey in slot.m.mods) {
-          slotMods.push({ id: Modifications.modifiers.indexOf(modKey), value: Math.round(slot.m.getModValue(modKey) * 10000) });
+          // Filter out invalid modifications
+          if (Modifications.validity[slot.m.grp] && Modifications.validity[slot.m.grp].indexOf(modKey) != -1) {
+            slotMods.push({ id: Modifications.modifiers.indexOf(modKey), value: slot.m.getModValue(modKey) });
+          }
         }
       }
       slots.push(slotMods);
@@ -1324,7 +1333,10 @@ export default class Ship {
       let slotMods = new Array();
       if (slot.m && slot.m.mods) {
         for (let modKey in slot.m.mods) {
-          slotMods.push({ id: Modifications.modifiers.indexOf(modKey), value: Math.round(slot.m.getModValue(modKey) * 10000) });
+          // Filter out invalid modifications
+          if (Modifications.validity[slot.m.grp] && Modifications.validity[slot.m.grp].indexOf(modKey) != -1) {
+            slotMods.push({ id: Modifications.modifiers.indexOf(modKey), value: slot.m.getModValue(modKey) });
+          }
         }
       }
       slots.push(slotMods);
@@ -1350,6 +1362,7 @@ export default class Ship {
           for (let slotMod of slot) {
             buffer.writeInt8(slotMod.id, curpos++);
             buffer.writeInt32LE(slotMod.value, curpos);
+            // console.log('ENCODE Slot ' + i + ': ' + Modifications.modifiers[slotMod.id] + ' = ' + slotMod.value);
             curpos += 4;
           }
           buffer.writeInt8(-1, curpos++);
@@ -1382,6 +1395,7 @@ export default class Ship {
       while (modificationId != -1) {
         let modificationValue = buffer.readInt32LE(curpos);
         curpos += 4;
+        // console.log('DECODE Slot ' + slot + ': ' + Modifications.modifiers[modificationId] + ' = ' + modificationValue);
         modifications[Modifications.modifiers[modificationId]] = modificationValue;
         modificationId = buffer.readInt8(curpos++);
       }