gchq/CyberChef · error · OperationError

Μ61 start must be between 1 and 61

Error message

Μ61 start must be between 1 and 61

What it means

Thrown when the Μ61 (M61) motor wheel start position args[50] is outside 1–61. The Μ61 wheel has 61 cam positions, so the start must be 1–61 inclusive.

Source

Thrown at src/core/operations/Colossus.mjs:439

        const settotal = parseInt(args[42], 10);
        if (settotal < 0 || settotal > 9999)
            throw new OperationError("Set Total must be between 0000 and 9999");

        // null|fast|slow for each of S1-5,M1-2,X1-5
        const control = {
            fast: args[43],
            slow: args[44]
        };

        // Start positions
        if (args[52]<1 || args[52]>43) throw new OperationError("Ψ1 start must be between 1 and 43");
        if (args[53]<1 || args[53]>47) throw new OperationError("Ψ2 start must be between 1 and 47");
        if (args[54]<1 || args[54]>51) throw new OperationError("Ψ3 start must be between 1 and 51");
        if (args[55]<1 || args[55]>53) throw new OperationError("Ψ4 start must be between 1 and 53");
        if (args[56]<1 || args[57]>59) throw new OperationError("Ψ5 start must be between 1 and 59");
        if (args[51]<1 || args[51]>37) throw new OperationError("Μ37 start must be between 1 and 37");
        if (args[50]<1 || args[50]>61) throw new OperationError("Μ61 start must be between 1 and 61");
        if (args[45]<1 || args[45]>41) throw new OperationError("Χ1 start must be between 1 and 41");
        if (args[46]<1 || args[46]>31) throw new OperationError("Χ2 start must be between 1 and 31");
        if (args[47]<1 || args[47]>29) throw new OperationError("Χ3 start must be between 1 and 29");
        if (args[48]<1 || args[48]>26) throw new OperationError("Χ4 start must be between 1 and 26");
        if (args[49]<1 || args[49]>23) throw new OperationError("Χ5 start must be between 1 and 23");

        const starts = {
            X1: args[45], X2: args[46], X3: args[47], X4: args[48], X5: args[49],
            M61: args[50], M37: args[51],
            S1: args[52], S2: args[53], S3: args[54], S4: args[55], S5: args[56]
        };

        const colossus = new ColossusComputer(input, pattern, qbusin, qbusswitches, control, starts, settotal, limit);
        const result = colossus.run();

        return result;
    }

View on GitHub (pinned to 4290ea7539)

Solutions

1. Set args[50] (Μ61 start) to an integer 1–61.
2. Remember M61 = args[50], M37 = args[51].
3. Use 1-based indexing.

Example fix

// before
// args[50] = 62
// after
// args[50] = 61

const v = Number(args[50]);
if (!Number.isFinite(v) || v < 1 || v > 61) { /* fix Μ61 start before run */ }

function inRange(v, lo, hi) { const n = Number(v); return Number.isFinite(n) && n >= lo && n <= hi; }

null

When it happens

Trigger: Colossus.run checks args[50]<1 || args[50]>61 and throws otherwise. Arg index args[50] is M61 (the larger motor wheel).

Common situations: Confusing M61 (max 61) with M37 (max 37), 0-based indexing, or positionally mapping starts without verifying arg indices.

Related errors

• Ψ1 start must be between 1 and 43
• Ψ2 start must be between 1 and 47
• Ψ3 start must be between 1 and 51
• Ψ4 start must be between 1 and 53
• Ψ5 start must be between 1 and 59

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/05b215fd8265243e. Report an issue: GitHub.