diff --git a/static/filterWeapons.js b/static/filterWeapons.js
index 8fe50bc..39c6085 100644
--- a/static/filterWeapons.js
+++ b/static/filterWeapons.js
@@ -29,6 +29,16 @@ let allWeapons = [];
 let currentWeaponTypes = [];
 let currentOperativeCategory = null;
 
+const normalizeToArray = (value) => {
+    if (!value) {
+        return [];
+    }
+    if (Array.isArray(value)) {
+        return value.filter(Boolean);
+    }
+    return [value].filter(Boolean);
+};
+
 const numberOrNull = (value) => {
     const parsed = Number.parseFloat(value);
     return Number.isFinite(parsed) ? parsed : null;
@@ -43,23 +53,39 @@ const formatValue = (value, suffix = '') => {
 };
 
 const matchesOperative = (modifierOperative) => {
-    if (!modifierOperative) {
+    const required = normalizeToArray(modifierOperative);
+    if (!required.length) {
         return true;
     }
     if (!currentOperativeCategory) {
         return false;
     }
-    return modifierOperative.toLowerCase() === currentOperativeCategory.toLowerCase();
+    const operative = currentOperativeCategory.toLowerCase();
+    return required.some((entry) => entry.toLowerCase() === operative);
 };
 
 const matchesWeaponType = (appliesTo) => {
-    if (!appliesTo) {
+    const required = normalizeToArray(appliesTo);
+    if (!required.length) {
         return true;
     }
     if (!currentWeaponTypes.length) {
         return false;
     }
-    return currentWeaponTypes.map((type) => type.toUpperCase()).includes(appliesTo.toUpperCase());
+    const available = currentWeaponTypes.map((type) => type.toUpperCase());
+    return required.some((type) => available.includes(type.toUpperCase()));
+};
+
+const matchesWeaponExclusion = (appliesNotTo) => {
+    const excluded = normalizeToArray(appliesNotTo);
+    if (!excluded.length) {
+        return true;
+    }
+    if (!currentWeaponTypes.length) {
+        return true;
+    }
+    const available = currentWeaponTypes.map((type) => type.toUpperCase());
+    return !excluded.some((type) => available.includes(type.toUpperCase()));
 };
 
 const applyBuffValue = (current, value, buffType) => {
@@ -79,7 +105,11 @@ const applyModifierToStats = (modifier, stats) => {
     if (!modifier) {
         return stats;
     }
-    if (!matchesOperative(modifier.operatives) || !matchesWeaponType(modifier.appliesTo)) {
+    if (
+        !matchesOperative(modifier.operatives)
+        || !matchesWeaponType(modifier.appliesTo)
+        || !matchesWeaponExclusion(modifier.appliesNotTo)
+    ) {
         return stats;
     }
 
@@ -141,17 +171,18 @@ const updateActiveModifierList = (modifiers) => {
 const calculate = () => {
     const data = new FormData(form);
     const baseDamage = numberOrNull(data.get('baseDamage'));
-    const projectiles = numberOrNull(data.get('projectiles')) ?? 1;
+    const projectilesRaw = numberOrNull(data.get('projectiles'));
+    const projectiles = projectilesRaw !== null ? Math.max(projectilesRaw, 1) : 1;
     const rpm = numberOrNull(data.get('rpm'));
     const magazine = numberOrNull(data.get('magazine'));
     const reload = numberOrNull(data.get('reload'));
     const targetHealth = numberOrNull(data.get('targetHealth'));
 
-    if (!baseDamage || !rpm) {
+    if (baseDamage === null || rpm === null || baseDamage < 0 || rpm <= 0) {
         Object.values(outputs).forEach((node) => {
             node.textContent = '--';
         });
-        updateActiveModifierList([]);
+        updateActiveModifierList(getSelectedModifiers());
         return;
     }
 
@@ -165,19 +196,31 @@ const calculate = () => {
         }
     );
 
-    const shotDamage = stats.damage * projectiles;
-    const shotsPerSecond = stats.rpm / 60;
+    const safeStats = {
+        damage: Math.max(stats.damage, 0),
+        rpm: Math.max(stats.rpm, 0),
+        reload: Number.isFinite(stats.reload) ? Math.max(stats.reload, 0) : stats.reload
+    };
+
+    const magazineSize = Number.isFinite(magazine) && magazine > 0 ? magazine : null;
+    const shotDamage = safeStats.damage * projectiles;
+    const shotsPerSecond = safeStats.rpm / 60;
     const burstDps = shotDamage * shotsPerSecond;
-    const magDamage = magazine ? shotDamage * magazine : null;
-    const timeToEmpty = magazine ? magazine / shotsPerSecond : null;
+    const magDamage = magazineSize ? shotDamage * magazineSize : null;
+    const timeToEmpty = magazineSize ? magazineSize / shotsPerSecond : null;
 
     let sustainedDps = null;
-    if (magDamage !== null && stats.reload !== null && timeToEmpty !== null && (timeToEmpty + stats.reload) > 0) {
-        sustainedDps = magDamage / (timeToEmpty + stats.reload);
+    if (
+        magDamage !== null
+        && Number.isFinite(safeStats.reload)
+        && timeToEmpty !== null
+        && (timeToEmpty + safeStats.reload) > 0
+    ) {
+        sustainedDps = magDamage / (timeToEmpty + safeStats.reload);
     }
 
     let ttk = null;
-    if (targetHealth && burstDps > 0) {
+    if (targetHealth !== null && targetHealth >= 0 && burstDps > 0) {
         ttk = targetHealth / burstDps;
     }
 
@@ -220,7 +263,8 @@ const normalizeModifier = (modifier, fallbackLabel) => {
         id: modifier.id,
         label: modifier.label ?? fallbackLabel ?? 'Unnamed modifier',
         operatives: modifier.operatives,
-        appliesTo: modifier.appliesTo
+        appliesTo: modifier.appliesTo,
+        appliesNotTo: modifier.appliesNotTo
     };
 
     if (Number.isFinite(modifier.value) && modifier.type) {
@@ -241,7 +285,7 @@ const inferSlot = (weapon) => {
         return directSlot;
     }
 
-    const types = weapon.types ?? weapon.guntype ?? [];
+    const types = normalizeToArray(weapon.types ?? weapon.guntype ?? []);
     if (types.includes('SECONDARY')) {
         return 'SECONDARY';
     }
@@ -251,18 +295,21 @@ const inferSlot = (weapon) => {
     return 'PRIMARY';
 };
 
-const normalizeWeapon = (weapon) => ({
-    id: weapon.id ?? weapon.name,
-    name: weapon.name,
-    damage: weapon.damage,
-    projectiles: weapon.projectiles ?? weapon.damage_multiplier ?? 1,
-    rpm: weapon.rpm,
-    magazine: weapon.magazine ?? weapon.mag_size,
-    reload: weapon.reload ?? weapon.reload_time,
-    types: weapon.types ?? weapon.guntype ?? [],
-    slot: inferSlot(weapon),
-    operatives: Array.isArray(weapon.operatives) ? weapon.operatives : []
-});
+const normalizeWeapon = (weapon) => {
+    const types = normalizeToArray(weapon.types ?? weapon.guntype ?? []);
+    return {
+        id: weapon.id ?? weapon.name,
+        name: weapon.name,
+        damage: weapon.damage,
+        projectiles: weapon.projectiles ?? weapon.damage_multiplier ?? 1,
+        rpm: weapon.rpm,
+        magazine: weapon.magazine ?? weapon.mag_size,
+        reload: weapon.reload ?? weapon.reload_time,
+        types,
+        slot: inferSlot(weapon),
+        operatives: Array.isArray(weapon.operatives) ? weapon.operatives : []
+    };
+};
 
 const selectedOperativeId = () => operativeSelect?.value ?? '';
 const selectedSlot = () => (loadoutSlotSelect?.value ?? 'primary').toUpperCase();
@@ -355,7 +402,10 @@ const createModifierOption = (modifier, container) => {
     if (!modifier || !container) {
         return;
     }
-    const id = modifier.id ?? `${modifier.label}-${Math.random().toString(36).slice(2)}`;
+    let id = modifier.id ?? `${modifier.label}-${Math.random().toString(36).slice(2)}`;
+    while (modifiersById.has(id)) {
+        id = `${id}-${Math.random().toString(36).slice(2)}`;
+    }
     modifiersById.set(id, modifier);
 
     const wrapper = document.createElement('label');
@@ -370,6 +420,9 @@ const createModifierOption = (modifier, container) => {
     if (modifier.appliesTo) {
         checkbox.dataset.appliesTo = modifier.appliesTo;
     }
+    if (modifier.appliesNotTo) {
+        checkbox.dataset.appliesNotTo = modifier.appliesNotTo;
+    }
 
     const label = document.createElement('span');
     label.textContent = modifier.label ?? 'Unnamed modifier';
@@ -479,10 +532,12 @@ const updateModifierAvailability = () => {
     checkboxes.forEach((checkbox) => {
         const requiredOperative = checkbox.dataset.operatives;
         const requiredType = checkbox.dataset.appliesTo;
+        const excludedType = checkbox.dataset.appliesNotTo;
         const wrapper = checkbox.closest('.af-checkbox');
         const operativeMatch = requiredOperative ? matchesOperative(requiredOperative) : true;
         const typeMatch = requiredType ? matchesWeaponType(requiredType) : true;
-        const isEnabled = operativeMatch && typeMatch;
+        const exclusionMatch = excludedType ? matchesWeaponExclusion(excludedType) : true;
+        const isEnabled = operativeMatch && typeMatch && exclusionMatch;
         checkbox.disabled = !isEnabled;
         if (wrapper) {
             wrapper.classList.toggle('is-disabled', !isEnabled);
diff --git a/static/style.css b/static/style.css
index 2c0d48a..4d352be 100644
--- a/static/style.css
+++ b/static/style.css
@@ -862,7 +862,7 @@ body.menu-open {
 }
 
 .af-details summary::before {
-    content: "▸";
+    content: ">";
     transition: transform 0.2s ease;
 }
 
diff --git a/templates/calculator.html b/templates/calculator.html
index c86cffe..543b065 100644
--- a/templates/calculator.html
+++ b/templates/calculator.html
@@ -58,12 +58,12 @@
         <div class="af-card af-card-builder">
             <div class="af-card-header">
                 <h2>Loadout builder</h2>
-                <p>Follow this flow: operative → slot → weapon → buffs. Results update right below.</p>
+                <p>Follow this flow: operative -> slot -> weapon -> buffs. Results update right below.</p>
             </div>
             <form class="af-form" id="af-calculator">
                 <div class="af-flow-grid">
                     <label>
-                        Step 1 · Operative
+                        Step 1 - Operative
                         <select id="af-operative-select" name="operativeSelect"
                                 data-source="{{ url_for('static', filename='json/operative.json') }}">
                             <option value="">No operative selected</option>
@@ -72,7 +72,7 @@
                     </label>
 
                     <label>
-                        Step 2 · Loadout slot
+                        Step 2 - Loadout slot
                         <select id="af-loadout-slot" name="loadoutSlot" disabled>
                             <option value="primary">Primary</option>
                             <option value="secondary">Secondary</option>
@@ -82,7 +82,7 @@
                     </label>
 
                     <label>
-                        Step 3 · Weapon
+                        Step 3 - Weapon
                         <select name="weaponSelect" id="af-weapon-select"
                                 data-source="{{ url_for('static', filename='json/data.json') }}">
                             <option value="">Custom entry</option>
@@ -253,3 +253,4 @@
 </script>
 </body>
 </html>
+