diff --git a/src/core/config/Categories.json b/src/core/config/Categories.json
index f663e16d..d731815b 100755
--- a/src/core/config/Categories.json
+++ b/src/core/config/Categories.json
@@ -110,7 +110,8 @@
             "Bombe",
             "Multiple Bombe",
             "Typex",
-            "Lorenz"
+            "Lorenz",
+            "Colossus"
         ]
     },
     {
diff --git a/src/core/lib/Colossus.mjs b/src/core/lib/Colossus.mjs
index 7fd67e2e..9301eb90 100644
--- a/src/core/lib/Colossus.mjs
+++ b/src/core/lib/Colossus.mjs
@@ -143,14 +143,11 @@ export class ColossusComputer {
         this.Xptr = [this.rotorPtrs.X1, this.rotorPtrs.X2, this.rotorPtrs.X3, this.rotorPtrs.X4, this.rotorPtrs.X5];
         this.Mptr = [this.rotorPtrs.M37, this.rotorPtrs.M61];
         this.Sptr = [this.rotorPtrs.S1, this.rotorPtrs.S2, this.rotorPtrs.S3, this.rotorPtrs.S4, this.rotorPtrs.S5];
-        // console.log(this.Xptr);
 
         // Run full loop of all character on the input tape (Z)
         for (let i=0; i<this.ciphertext.length; i++) {
             charZin = this.ciphertext.charAt(i);
 
-            // console.log('reading tape char #'+i+' : '+charZin);
-
             // Firstly, we check what inputs are specified on the Q-bus input switches
             this.getQbusInputs(charZin);
 
@@ -158,13 +155,13 @@ export class ColossusComputer {
              * Pattern conditions on individual impulses. Matching patterns of bits on the Q bus.
              * This is the top section on Colussus K rack - the Q bus programming switches
              */
-            this.runQbusProcessingConditional();
+            const tmpcnt = this.runQbusProcessingConditional();
 
             /*
              * Addition of impulses.
              * This is the bottom section of Colossus K rack.
              */
-            this.runQbusProcessingAddition();
+            this.runQbusProcessingAddition(tmpcnt);
 
             // Store Z bit impulse 5 two back required for P5 limitation
             this.P5Zbit[1] = this.P5Zbit[0];
@@ -191,14 +188,14 @@ export class ColossusComputer {
 
         // Get Chi rotor 5 two back to calculate plaintext (Z+Chi+Psi=Plain)
         let X5bPtr=this.Xptr[4]-1;
-        if (X5bPtr==0) X5bPtr=ROTOR_SIZES.X5;
+        if (X5bPtr===0) X5bPtr=ROTOR_SIZES.X5;
         X5bPtr=X5bPtr-1;
-        if (X5bPtr==0) X5bPtr=ROTOR_SIZES.X5;
+        if (X5bPtr===0) X5bPtr=ROTOR_SIZES.X5;
         // Get Psi rotor 5 two back to calculate plaintext (Z+Chi+Psi=Plain)
         let S5bPtr=this.Sptr[4]-1;
-        if (S5bPtr==0) S5bPtr=ROTOR_SIZES.S5;
+        if (S5bPtr===0) S5bPtr=ROTOR_SIZES.S5;
         S5bPtr=S5bPtr-1;
-        if (S5bPtr==0) S5bPtr=ROTOR_SIZES.S5;
+        if (S5bPtr===0) S5bPtr=ROTOR_SIZES.S5;
 
         const x2sw = this.limitations.X2;
         const s1sw = this.limitations.S1;
@@ -217,8 +214,6 @@ export class ColossusComputer {
             lim = lim ^ p5lim;
         }
 
-        // console.log(this.Mptr);
-        // console.log(this.rings.M[2]);
         const basicmotor = this.rings.M[2][this.Mptr[0]-1];
         this.totalmotor = basicmotor;
 
@@ -230,8 +225,6 @@ export class ColossusComputer {
             }
         }
 
-        // console.log('BM='+basicmotor+', TM='+this.totalmotor);
-
         // Step Chi rotors
         for (let r=0; r<5; r++) {
             this.Xptr[r]++;
@@ -239,7 +232,6 @@ export class ColossusComputer {
         }
 
         if (this.totalmotor) {
-            // console.log('step Psi');
             // Step Psi rotors
             for (let r=0; r<5; r++) {
                 this.Sptr[r]++;
@@ -263,81 +255,56 @@ export class ColossusComputer {
     getQbusInputs(charZin) {
         // Zbits - the bits from the current character from the cipher tape.
         this.Zbits = this.ITAlookup[charZin].split("");
-        // console.log('Zbits = '+this.Zbits);
         if (this.qbusin.Z === "Z") {
             // direct Z
             this.Qbits = this.Zbits;
-            // console.log('direct Z: Qbits = '+this.Qbits);
         } else if (this.qbusin.Z === "ΔZ") {
             // delta Z, the Bitwise XOR of this character Zbits + last character Zbits
             for (let b=0;b<5;b++) {
                 this.Qbits[b] = this.Zbits[b] ^ this.ZbitsOneBack[b];
             }
-
-            // console.log('delta Z: Qbits = '+this.Qbits);
         }
         this.ZbitsOneBack = this.Zbits.slice(); // copy value of object, not reference
 
-        // console.log('Zin::Q bus now '+this.Qbits+'['+this.ReverseITAlookup[this.Qbits.join("")]+']');
-
         // Xbits - the current Chi wheel bits
-        // console.log(this.rings.X);
-        // console.log('Xptr = '+this.Xptr);
-
         for (let b=0;b<5;b++) {
             this.Xbits[b] = this.rings.X[b+1][this.Xptr[b]-1];
         }
         if (this.qbusin.Chi !== "") {
-            // console.log('X Bits '+this.Xbits+'['+this.ReverseITAlookup[this.Xbits.join("")]+']');
-            // console.log('X Char = ' + this.ReverseITAlookup[this.Xbits.join("")]);
             if (this.qbusin.Chi === "Χ") {
                 // direct X added to Qbits
                 for (let b=0;b<5;b++) {
                     this.Qbits[b] = this.Qbits[b] ^ this.Xbits[b];
                 }
-                // console.log('direct X: Qbits = '+this.Qbits);
             } else if (this.qbusin.Chi === "ΔΧ") {
                 // delta X
                 for (let b=0;b<5;b++) {
                     this.Qbits[b] = this.Qbits[b] ^ this.Xbits[b];
                     this.Qbits[b] = this.Qbits[b] ^ this.XbitsOneBack[b];
                 }
-                // console.log('delta X: Xbits = '+this.Xbits+' Xbits-1 = '+this.XbitsOneBack);
-                // console.log('delta X: Qbits = '+this.Qbits);
             }
         }
         this.XbitsOneBack = this.Xbits.slice();
-        // console.log('setting XbitsOneBack to '+this.Xbits);
-
-        // console.log('Zin+Xin::Q bus now '+this.Qbits+'['+this.ReverseITAlookup[this.Qbits.join("")]+']');
 
         // Sbits - the current Psi wheel bits
-        // console.log(this.rings.S);
-        // console.log('Sptr = '+this.Sptr);
         for (let b=0;b<5;b++) {
             this.Sbits[b] = this.rings.S[b+1][this.Sptr[b]-1];
         }
         if (this.qbusin.Psi !== "") {
-            // console.log('S Bits '+this.Sbits+'['+this.ReverseITAlookup[this.Sbits.join("")]+']');
-            // console.log('S Char = ' + this.ReverseITAlookup[this.Sbits.join("")]);
             if (this.qbusin.Psi === "Ψ") {
                 // direct S added to Qbits
                 for (let b=0;b<5;b++) {
                     this.Qbits[b] = this.Qbits[b] ^ this.Sbits[b];
                 }
-                // console.log('direct S: Qbits = '+this.Qbits);
             } else if (this.qbusin.Psi === "ΔΨ") {
                 // delta S
                 for (let b=0;b<5;b++) {
                     this.Qbits[b] = this.Qbits[b] ^ this.Sbits[b];
                     this.Qbits[b] = this.Qbits[b] ^ this.SbitsOneBack[b];
                 }
-                // console.log('delta S: Qbits = '+this.Qbits);
             }
         }
         this.SbitsOneBack = this.Sbits.slice();
-
-        // console.log('Q bus now '+this.Qbits+'['+this.ReverseITAlookup[this.Qbits.join("")]+']');
     }
 
     /**
@@ -355,7 +322,7 @@ export class ColossusComputer {
                 const Qswitch = this.readBusSwitches(row.Qswitches);
                 // Match switches to bit pattern
                 for (let s=0;s<5;s++) {
-                    if (Qswitch[s] >= 0 && Qswitch[s] !== parseInt(this.Qbits[s],10)) result = false;
+                    if (Qswitch[s] >= 0 && Qswitch[s] !== parseInt(this.Qbits[s], 10)) result = false;
                 }
                 // Check for NOT switch
                 if (row.Negate) result = !result;
@@ -372,21 +339,21 @@ export class ColossusComputer {
         // Negate the whole column, this allows A OR B by doing NOT(NOT A AND NOT B)
         for (let c=0;c<5;c++) {
             if (this.qbusswitches.condNegateAll && cnt[c] !== -1) cnt[c] = !cnt[c];
-
-            if (this.qbusswitches.totalMotor === "" || (this.qbusswitches.totalMotor === "x" && this.totalmotor === 0) || (this.qbusswitches.totalMotor === "." && this.totalmotor === 1)) {
-                if (cnt[c] === true) this.allCounters[c]++;
-            }
-
         }
 
+        return cnt;
+
     }
 
     /**
      * Addition of impulses Q bus section
      */
-    runQbusProcessingAddition() {
+    runQbusProcessingAddition(cnt) {
         const row = this.qbusswitches.addition[0];
         const Qswitch = row.Qswitches.slice();
+
+        // To save making the arguments of this operation any larger, limiting addition counter to first one only
+        // Colossus could actually add into any of the five counters.
         if (row.C1) {
             let addition = 0;
             for (let s=0;s<5;s++) {
@@ -397,10 +364,24 @@ export class ColossusComputer {
             }
             const equals = (row.Equals===""?-1:(row.Equals==="."?0:1));
             if (addition === equals) {
-                this.allCounters[0]++;
+                // AND with conditional rows to get final result
+                if (cnt[0] === -1) cnt[0] = true;
+            } else {
+                cnt[0] = false;
             }
         }
-        // console.log("counter1="+this.allCounters[0]);
+
+        // Final check, check for addition section negate
+        // then, if any column set, from top to bottom of rack, add to counter.
+        for (let c=0;c<5;c++) {
+            if (this.qbusswitches.addNegateAll && cnt[c] !== -1) cnt[c] = !cnt[c];
+
+            if (this.qbusswitches.totalMotor === "" || (this.qbusswitches.totalMotor === "x" && this.totalmotor === 0) || (this.qbusswitches.totalMotor === "." && this.totalmotor === 1)) {
+                if (cnt[c] === true) this.allCounters[c]++;
+            }
+
+        }
+
     }
 
     /**
diff --git a/src/core/operations/Colossus.mjs b/src/core/operations/Colossus.mjs
index 896252dd..260616b2 100644
--- a/src/core/operations/Colossus.mjs
+++ b/src/core/operations/Colossus.mjs
@@ -17,13 +17,13 @@ import { SWITCHES, VALID_ITA2 } from "../lib/Lorenz.mjs";
 class Colossus extends Operation {
 
     /**
-     * Lorenz constructor
+     * Colossus constructor
      */
     constructor() {
         super();
         this.name = "Colossus";
         this.module = "Bletchley";
-        this.description = "Colossus ... ";
+        this.description = "Colossus is the name of the world's first electronic computer. Ten computers were designed by Tommy Flowers and built at the Post Office Research Labs at Dollis Hill in 1943 during World War 2. They assisted with the breaking of the German Lorenz cipher attachment, a machine created to encipher communications between Hitler and his generals on the front lines.<br><br>To learn more, Virtual Colossus, an online, browser based simulation of a Colossus computer is available at <a href='https://virtualcolossus.co.uk' target='_blank'>https://virtualcolossus.co.uk</a>.<br><br>A more detailed description of this operation can be found <a href='https://github.com/VirtualColossus/CyberChef/wiki/Colossus' target='_blank'>here</a>.";
         this.infoURL = "https://wikipedia.org/wiki/Colossus_computer";
         this.inputType = "string";
         this.outputType = "JSON";
@@ -438,8 +438,6 @@ class Colossus extends Operation {
         const colossus = new ColossusComputer(input, pattern, qbusin, qbusswitches, control, starts, settotal, limit);
         const result = colossus.run();
 
-        console.log(result);
-
         return result;
 
     }
@@ -553,9 +551,6 @@ class Colossus extends Operation {
      * @returns {html}
      */
     present(output) {
-        console.log("output="+ typeof(output));
-        console.log("counters="+ typeof(output.counters));
-
         let html = "Colossus Printer\n\n";
         html += output.printout + "\n\n";
         html += "Colossus Counters\n\n";
diff --git a/tests/operations/index.mjs b/tests/operations/index.mjs
index c54fa7ef..8c80ff99 100644
--- a/tests/operations/index.mjs
+++ b/tests/operations/index.mjs
@@ -93,6 +93,7 @@ import "./tests/DefangIP.mjs";
 import "./tests/ParseUDP.mjs";
 import "./tests/AvroToJSON.mjs";
 import "./tests/Lorenz.mjs";
+import "./tests/Colossus.mjs";
 
 
 // Cannot test operations that use the File type yet