{"record":{"id":"a44b385b13b34fdb","repo":"gchq/CyberChef","slug":"37-start-must-be-between-1-and-37","errorCode":null,"errorMessage":"Μ37 start must be between 1 and 37","messagePattern":"Μ37 start must be between 1 and 37","errorType":"exception","errorClass":"OperationError","httpStatus":null,"severity":"error","filePath":"src/core/operations/Colossus.mjs","lineNumber":438,"sourceCode":"        };\n\n        const settotal = parseInt(args[42], 10);\n        if (settotal < 0 || settotal > 9999)\n            throw new OperationError(\"Set Total must be between 0000 and 9999\");\n\n        // null|fast|slow for each of S1-5,M1-2,X1-5\n        const control = {\n            fast: args[43],\n            slow: args[44]\n        };\n\n        // Start positions\n        if (args[52]<1 || args[52]>43) throw new OperationError(\"Ψ1 start must be between 1 and 43\");\n        if (args[53]<1 || args[53]>47) throw new OperationError(\"Ψ2 start must be between 1 and 47\");\n        if (args[54]<1 || args[54]>51) throw new OperationError(\"Ψ3 start must be between 1 and 51\");\n        if (args[55]<1 || args[55]>53) throw new OperationError(\"Ψ4 start must be between 1 and 53\");\n        if (args[56]<1 || args[57]>59) throw new OperationError(\"Ψ5 start must be between 1 and 59\");\n        if (args[51]<1 || args[51]>37) throw new OperationError(\"Μ37 start must be between 1 and 37\");\n        if (args[50]<1 || args[50]>61) throw new OperationError(\"Μ61 start must be between 1 and 61\");\n        if (args[45]<1 || args[45]>41) throw new OperationError(\"Χ1 start must be between 1 and 41\");\n        if (args[46]<1 || args[46]>31) throw new OperationError(\"Χ2 start must be between 1 and 31\");\n        if (args[47]<1 || args[47]>29) throw new OperationError(\"Χ3 start must be between 1 and 29\");\n        if (args[48]<1 || args[48]>26) throw new OperationError(\"Χ4 start must be between 1 and 26\");\n        if (args[49]<1 || args[49]>23) throw new OperationError(\"Χ5 start must be between 1 and 23\");\n\n        const starts = {\n            X1: args[45], X2: args[46], X3: args[47], X4: args[48], X5: args[49],\n            M61: args[50], M37: args[51],\n            S1: args[52], S2: args[53], S3: args[54], S4: args[55], S5: args[56]\n        };\n\n        const colossus = new ColossusComputer(input, pattern, qbusin, qbusswitches, control, starts, settotal, limit);\n        const result = colossus.run();\n\n        return result;\n    }","sourceCodeStart":420,"sourceCodeEnd":456,"githubUrl":"https://github.com/gchq/CyberChef/blob/4290ea753912378913b1f3f54e0fc5720afeda5d/src/core/operations/Colossus.mjs#L420-L456","documentation":"Thrown when the Μ37 (M37) motor wheel start position args[51] is outside 1–37. The Μ37 wheel has 37 cam positions, so the start must be 1–37 inclusive.","triggerScenarios":"Colossus.run checks args[51]<1 || args[51]>37 and throws otherwise. Note arg indexing is non-sequential (M37 is args[51], M61 is args[50]).","commonSituations":"User confuses the two motor wheels (M37 vs M61) and their ranges, uses 0-based indexing, or maps starts positionally without checking which arg index each wheel occupies.","solutions":["Set args[51] (Μ37 start) to an integer 1–37.","Mind arg index: M37 = args[51], M61 = args[50] (reverse of numeric order).","Use 1-based indexing."],"exampleFix":"// before\n// args[51] = 38\n// after\n// args[51] = 37","handlingStrategy":"validation","validationCode":"const v = Number(args[51]);\nif (!Number.isFinite(v) || v < 1 || v > 37) { /* fix Μ37 start before run */ }","typeGuard":"function inRange(v, lo, hi) { const n = Number(v); return Number.isFinite(n) && n >= lo && n <= hi; }","tryCatchPattern":"null","preventionTips":["Use 1-based indexing (M37 max = 37).","Mind arg index: M37 = args[51], M61 = args[50].","Validate per-wheel ranges before running."],"tags":["colossus","wheel-start","numeric-range","input-validation"],"backgroundTag":null,"analyzedSha":"4290ea753912378913b1f3f54e0fc5720afeda5d","analyzedAt":"2026-08-13T06:05:50.210Z","schemaVersion":2},"datasetVersion":"2026-08-13T09:17:06.757Z"}