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Error Checking

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Error checking tests measure your ability to compare data sets and identify discrepancies. You'll compare numbers, codes, and text to find where differences occur between an original and a copy.

These tests assess attention to detail and accuracy under time pressure—essential skills for data entry, accounting, quality control, and administrative roles. Our procedurally generated comparisons include transpositions, substitutions, and missing characters at varying difficulty levels, ensuring unlimited unique practice.

All comparisons are generated locally in your browser. Your progress and answers are stored only on your device — we never collect any personal data.

Key Patterns & Formats

Transposition Errors

Adjacent characters are swapped in position.

Original: ABCD → Error: ABDC (C and D swapped)

Substitution Errors

One character is replaced with a different character.

Original: ABCD → Error: ABXD (C replaced with X)

Omission Errors

One or more characters are missing from the data.

Original: ABCD → Error: ABD (C omitted)

Addition Errors

Extra characters are accidentally inserted into the data.

Original: ABCD → Error: ABCXD (X inserted)

Double Transposition

Two separate pairs of adjacent characters are swapped.

Original: ABCDEF → Error: BADCEF (AB swapped AND CD swapped)

Visual Confusion

Similar-looking characters are mistaken for each other.

Common pairs: B↔8, O↔0, I↔1, S↔5, G↔6, Z↔2

Keyboard Proximity

A character is replaced by an adjacent key on the keyboard.

Key replaced by horizontally or vertically adjacent key on QWERTY layout

Repeated Character

A character is accidentally typed twice in succession.

Original character at position N is duplicated: ABC → ABBC

Reversal

A sequence of 3 or more adjacent characters is reversed.

Substring ABC becomes CBA within the string

Spacing Error

An unwanted space is inserted into the string.

Space inserted at position N: ABCD → AB CD

Format Shift

A separator or delimiter is moved to an incorrect position.

Separator moves from position M to position N: AB-1234 → A-B1234

Phonetic Substitution

A character is replaced by a similar-sounding character.

Common pairs: C↔K, F↔V, M↔N, B↔P, D↔T, G↔J

Case Flip

A letter's case is changed from uppercase to lowercase or vice versa.

Uppercase letter becomes lowercase (A→a) or lowercase becomes uppercase (a→A)

Solving Strategies

  • Same characters, but two adjacent ones are in reversed order
  • Length remains the same
  • Often occurs in the middle of strings
  • One character is different, all others match
  • Often involves similar-looking characters
  • Copy is shorter than original
  • All present characters match, one is missing
  • Check length first as quick filter

Common Pitfalls

  • Confusing transposition with substitution
  • Missing subtle swaps in long strings
  • Not checking adjacent pairs systematically
  • Confusing substitution with transposition
  • Missing errors with visually similar characters (0/O, 1/l/I)
  • Not comparing character by character

Frequently Asked Questions

Look for transpositions (1234 vs 1324), substitutions (1234 vs 1284), missing characters (1234 vs 134), and extra characters (1234 vs 12345). Errors are subtle, so check each character carefully.
Banks, accounting firms, insurance companies, law firms, healthcare organizations, and any role involving data entry or document processing. SHL, Talent Q, and Cubiks all offer error checking assessments.
Scan systematically row by row, character by character. Use a finger or cursor to track position. Focus on one row at a time. Practice improves speed and accuracy—aim for zero errors before speeding up.
Each comparison is procedurally generated using realistic data formats including numbers, alphanumeric codes, and text strings. The system introduces specific error types — transpositions, substitutions, insertions, and deletions — at controlled rates based on the difficulty level. This ensures every practice set is unique and has a single correct answer.

Sources & References

Transposition Errors

Transposition Error
3 4 5","compare":"1 2 4 3 5","errorType":"Adjacent swap at positions 3-4"}'>
Find the error: Original '12345' vs Given '12435'
  1. 1
    Compare position 1: '1' = '1' ✓Match
  2. 2
    Compare position 2: '2' = '2' ✓Match
  3. 3
    Compare position 3: '3' vs '4' - mismatch found!3 ≠ 4
  4. 4
    Compare position 4: '4' vs '3' - mismatch found!4 ≠ 3
  5. 5
    Compare position 5: '5' = '5' ✓Match
  6. 6
    Pattern: positions 3 and 4 contain swapped characters34 ↔ 43
Refs:Data Entry Error Types

Substitution Errors

Substitution Errors
Original: ABCD → Error: ABXD (C replaced with X)
12345 → 12845 (3 replaced with 8)
JOHNSON → JOHNS0N (O replaced with zero)
AB-1234 → AB-1284 (3 replaced with 8)
Find the error: Original 'JOHNSON' vs Given 'JOHNS0N'
  1. 1
    Compare position 1: 'J' = 'J'J
  2. 2
    Compare position 2: 'O' = 'O'O
  3. 3
    Compare position 3: 'H' = 'H'H
  4. 4
    Compare position 4: 'N' = 'N'N
  5. 5
    Compare position 5: 'S' = 'S'S
  6. 6
    Compare position 6: 'O' vs '0' - mismatch foundO vs 0
  7. 7
    Compare position 7: 'N' = 'N'N
  8. 8
    The letter 'O' was replaced with the digit '0' (zero)O replaced by 0
Refs:Character Recognition Error Patterns

Omission Errors

Omission Errors
Original: ABCD → Error: ABD (C omitted)
123456 → 12346 (5 omitted)
WILLIAMS → WILLAMS (I omitted)
AB-1234 → AB-124 (3 omitted)
Find the error: Original '123456' vs Given '12346'
  1. 1
    Check lengths: original has 6 characters, given has 56 vs 5
  2. 2
    Compare position 1: '1' = '1'1
  3. 3
    Compare position 2: '2' = '2'2
  4. 4
    Compare position 3: '3' = '3'3
  5. 5
    Compare position 4: '4' = '4'4
  6. 6
    Compare position 5: '5' vs '6' - mismatch, '5' is missing5 missing
  7. 7
    The digit '5' was omitted from position 55 omitted
Refs:Typing Error Classification

Addition Errors

Addition Errors
Original: ABCD → Error: ABCXD (X inserted)
12345 → 123345 (extra 3 inserted)
SMITH → SMIITH (extra I inserted)
AB-1234 → AB-12334 (extra 3 inserted)
Find the error: Original '12345' vs Given '123345'
  1. 1
    Check lengths: original has 5 characters, given has 65 vs 6
  2. 2
    Compare position 1: '1' = '1'1
  3. 3
    Compare position 2: '2' = '2'2
  4. 4
    Compare position 3: '3' = '3'3
  5. 5
    Compare position 4: '4' vs '3' - extra character foundextra 3
  6. 6
    An extra '3' was inserted at position 43 inserted
Refs:Input Validation Best Practices

Double Transposition

Double Transposition
Original: ABCDEF → Error: BADCEF (AB swapped AND CD swapped)
123456 → 213465 (12 swapped AND 45 swapped)
ABCDEF → BACDEF → BADCEF (two transpositions)
AB-1234 → BA-1324 (AB swapped AND 23 swapped)
Find the error: Original '123456' vs Given '213465'
  1. 1
    Compare position 1: '1' vs '2' - mismatch1 vs 2
  2. 2
    Compare position 2: '2' vs '1' - mismatch2 vs 1
  3. 3
    First swap identified: '1' and '2' are transposed12 vs 21
  4. 4
    Compare position 3: '3' = '3'3
  5. 5
    Compare position 4: '4' vs '4'4
  6. 6
    Compare position 5: '5' vs '6' - mismatch5 vs 6
  7. 7
    Compare position 6: '6' vs '5' - mismatch6 vs 5
  8. 8
    Second swap identified: '5' and '6' are transposed56 vs 65

Visual Confusion

Visual Confusion
Common pairs: B↔8, O↔0, I↔1, S↔5, G↔6, Z↔2
AB-1234 → A8-1234 (B confused with 8)
CODE01 → CODEO1 (0 confused with O)
SIGNAL → 5IGNAL (S confused with 5)
Find the error: Original 'AB-1234' vs Given 'A8-1234'
  1. 1
    Compare position 1: 'A' = 'A'A
  2. 2
    Compare position 2: 'B' vs '8' - mismatch foundB vs 8
  3. 3
    Compare position 3: '-' = '-'-
  4. 4
    Compare remaining: '1234' = '1234'1234
  5. 5
    The letter 'B' was confused with the digit '8'B confused with 8
  6. 6
    These characters look similar: B and 8 have similar shapesB ↔ 8
Refs:OCR Accuracy and Character Confusion

Keyboard Proximity

Keyboard Proximity
Key replaced by horizontally or vertically adjacent key on QWERTY layout
HELLO → HRLLO (E replaced by adjacent R)
12345 → 12445 (3 replaced by adjacent 4)
CODE → CODW (E replaced by adjacent W)
Find the error: Original 'HELLO' vs Given 'HRLLO'
  1. 1
    Compare position 1: 'H' = 'H'H
  2. 2
    Compare position 2: 'E' vs 'R' - mismatch foundE vs R
  3. 3
    Compare position 3: 'L' = 'L'L
  4. 4
    Compare position 4: 'L' = 'L'L
  5. 5
    Compare position 5: 'O' = 'O'O
  6. 6
    Check keyboard layout: 'E' and 'R' are adjacent on QWERTY keyboardE adjacent to R
  7. 7
    The typist hit 'R' instead of 'E' due to finger placementE → R

Repeated Character

Repeated Character
Original character at position N is duplicated: ABC → ABBC
12345 → 123345 (3 repeated)
HELLO → HELLLO (L repeated)
AB-1234 → AB-12234 (2 repeated)
Find the error: Original 'HELLO' vs Given 'HELLLO'
  1. 1
    Check lengths: original has 5 characters, given has 65 vs 6
  2. 2
    Compare position 1: 'H' = 'H'H
  3. 3
    Compare position 2: 'E' = 'E'E
  4. 4
    Compare position 3: 'L' = 'L'L
  5. 5
    Compare position 4: 'L' = 'L'L
  6. 6
    Compare position 5: 'O' vs 'L' - extra 'L' foundextra L
  7. 7
    The letter 'L' was typed twice at position 4L repeated

Reversal

Reversal
Substring ABC becomes CBA within the string
123456 → 132456 (123 reversed to 321, shown as 132)
ABCDEF → ACBDEF (BCD reversed)
AB-1234 → AB-3214 (1234 partially reversed)
Find the error: Original 'AB-1234' vs Given 'AB-3214'
  1. 1
    Compare prefix: 'AB-' = 'AB-'AB-
  2. 2
    Compare position 4: '1' vs '3' - mismatch1 vs 3
  3. 3
    Compare position 5: '2' = '2'2
  4. 4
    Compare position 6: '3' vs '1' - mismatch3 vs 1
  5. 5
    Compare position 7: '4' = '4'4
  6. 6
    Pattern identified: '123' was reversed to '321'123 → 321
  7. 7
    This is a 3-character reversal, not simple transpositionreversal pattern

Spacing Error

Spacing Error
Space inserted at position N: ABCD → AB CD
12345 → 123 45 (space inserted)
HELLO → HEL LO (space in middle)
AB-1234 → AB- 1234 (space after hyphen)
Find the error: Original '12345' vs Given '123 45'
  1. 1
    Check lengths: original has 5 characters, given has 65 vs 6
  2. 2
    Compare position 1: '1' = '1'1
  3. 3
    Compare position 2: '2' = '2'2
  4. 4
    Compare position 3: '3' = '3'3
  5. 5
    Compare position 4: '4' vs ' ' - space foundspace inserted
  6. 6
    An unwanted space was inserted after position 3123 | 45
  7. 7
    The remaining characters '45' are shifted by one position45 shifted

Format Shift

Format Shift
Separator moves from position M to position N: AB-1234 → A-B1234
AB-1234 → A-B1234 (hyphen shifted left)
AB-1234 → ABC-234 (hyphen shifted right)
12-34-56 → 123-4-56 (hyphen repositioned)
Find the error: Original 'AB-1234' vs Given 'A-B1234'
  1. 1
    Compare position 1: 'A' = 'A'A
  2. 2
    Compare position 2: 'B' vs '-' - mismatchB vs -
  3. 3
    Compare position 3: '-' vs 'B' - mismatch- vs B
  4. 4
    The hyphen moved from position 3 to position 2hyphen shifted
  5. 5
    All characters are present but separator is misplacedformat changed
  6. 6
    Original format: 'AB-1234' (2 letters, hyphen, 4 digits)AB-1234
  7. 7
    Error format: 'A-B1234' (1 letter, hyphen, 1 letter, 4 digits)A-B1234

Phonetic Substitution

Phonetic Substitution
Common pairs: C↔K, F↔V, M↔N, B↔P, D↔T, G↔J
PACK → BACK (P confused with B)
CAME → KAME (C confused with K)
FIVE → VIVE (F confused with V)
Find the error: Original 'PACK' vs Given 'BACK'
  1. 1
    Compare position 1: 'P' vs 'B' - mismatch foundP vs B
  2. 2
    Compare position 2: 'A' = 'A'A
  3. 3
    Compare position 3: 'C' = 'C'C
  4. 4
    Compare position 4: 'K' = 'K'K
  5. 5
    The letter 'P' was replaced with 'B'P → B
  6. 6
    These are phonetically similar: both are bilabial stopsP ↔ B
  7. 7
    Common when transcribing from spoken dictationphonetic pair

Case Flip

Case Flip
Uppercase letter becomes lowercase (A→a) or lowercase becomes uppercase (a→A)
HELLO → HeLLO (E became lowercase)
AB-1234 → Ab-1234 (B became lowercase)
CODE → COdE (D became lowercase)
Find the error: Original 'HELLO' vs Given 'HeLLO'
  1. 1
    Compare position 1: 'H' = 'H' (both uppercase)H
  2. 2
    Compare position 2: 'E' vs 'e' - case mismatch foundE vs e
  3. 3
    Compare position 3: 'L' = 'L' (both uppercase)L
  4. 4
    Compare position 4: 'L' = 'L' (both uppercase)L
  5. 5
    Compare position 5: 'O' = 'O' (both uppercase)O
  6. 6
    The uppercase 'E' became lowercase 'e'E → e
  7. 7
    Likely caused by Shift key release at wrong timecase flip