01 | A PLAUSIBLE VALUE CAN STILL BE COPIED WRONGLY

A student’s paper test result is 34 out of 50. When transferring it into a computer, a teacher types 43.

The entered value is present, is a whole number and is within zero to fifty. Those validation checks pass, but the copied value does not match the source.

Verification checks that data has been copied or entered as intended. In this example, it helps check that the stored mark agrees with the mark on the paper.

The syllabus includes two methods: visual checking and double entry. Both can detect some entry errors, but neither guarantees that the original information was factually correct.

This lesson starts with the source and entered value, then follows what each method actually compares.

02 | IDENTIFY THE SOURCE AND THE ENTERED DATA

The source is the information being copied or used as the reference. It could be a paper form, a document, a label or another recorded value.

The entered data is the value supplied to the destination system. Verification compares representations of the intended information, rather than deciding whether it meets an accepted numeric range.

The records refer to the same student, but the marks differ.

For a visual check, the source and entered data must be available together or in a way that permits reliable comparison. Looking at the entered mark alone and deciding that it “seems reasonable” does not establish that it matches the paper.

Also check the record association. A correct mark placed beside the wrong student is a transfer error even when the digits themselves were copied correctly.

03 | VISUAL CHECK: COMPARE WITH THE SOURCE

A visual check is when a person compares the entered data with the original or intended source to look for discrepancies.

For the mark example, read the student’s identifier on the paper, find the same student’s computer record and compare the entered mark with the source mark. Thirty-four and forty-three do not match, so the entry needs correction.

For a code such as AB1042, compare every character in its position. AB1402 contains the same characters but in a different order; a careful comparison reveals the difference.

After a correction, check again. Changing one character does not automatically prove the whole record now matches.

A visual check is a human comparison process. It is not a check where the computer decides that an input has the right appearance or character pattern; that would be format validation.

04 | MAKE THE COMPARISON SYSTEMATIC

Long codes are easy to misread if you skim them. Work through the identifier in order, using the same character positions in the source and destination.

Check labels as well as values: is this the same student, the same date and the same field? If a form contains both a home and an emergency number, matching digits to the wrong field is still a problem.

Good layout can support the task by keeping the source and entered value close together and making field labels readable. It does not remove the need for careful comparison.

Some situations use another person to carry out the check, reducing reliance on the original typist’s assumptions. However, the method remains a visual check whether the original person or another person performs it.

The goal is matching the source, not merely finding values that look plausible.

05 | VISUAL CHECKING HAS LIMITS

A person can miss a discrepancy, especially when the source is unclear, the data is long or many records must be checked. Similar characters such as O and 0 can be difficult to distinguish.

If the source itself is wrong, a perfect comparison can confirm a perfect copy of wrong information. For example, a source mark recorded as 43 when the correct mark was 34 can be faithfully entered as 43.

A visual check also takes time and depends on the person’s attention. It is useful when a readable source is available, but should not be described as automatically detecting every typing error.

A clear limitation is: “The check compares entered data with its source, so it can detect copying discrepancies, but it cannot establish that the source was factually correct.”

06 | DOUBLE ENTRY: RECEIVE THE DATA TWICE

Double-entry verification receives the same intended data twice and compares the two entries. If they differ, the system flags the mismatch and asks for correction or re-entry.

Suppose the intended code is AB1042. The first entry is AB1402 and the second is AB1042. Their characters differ, so the system detects a mismatch.

If both entries are AB1042, they agree. The check establishes consistency between the entries; it does not necessarily establish agreement with an independent original source.

Double entry can be performed by the same person entering the data again or by different people entering it separately. The defining feature is the two entries and their comparison, not the number of people involved.

Typing an email address twice or confirming a newly chosen password are familiar examples. This checks agreement with the intended entry, not whether an email mailbox exists or a password meets security rules.

07 | SEE WHAT MATCHING AND MISMATCHING MEAN

Assume the intended code is AB1042. Consider these pairs of entries.

The matching wrong pair is the important limitation: AB1402 entered twice passes a simple equality comparison despite differing from the intended code.

Independent re-entry reduces the chance that the second entry simply reproduces the first error. Copying the first field into the second reproduces its contents, including any mistake, so it adds little checking evidence.

A mismatch does not tell the system which entry is correct. The first could be correct, the second could be correct, or both could differ from the intended value.

08 | READ A SIMPLE DOUBLE-ENTRY ALGORITHM

This example compares two text entries exactly. Text is appropriate because an identifier’s characters and any leading zeros need to be preserved.

DECLARE FirstEntry : STRING
DECLARE SecondEntry : STRING
OUTPUT "Enter the identifier"
INPUT FirstEntry
OUTPUT "Enter the identifier again independently"
INPUT SecondEntry
IF FirstEntry = SecondEntry
  THEN
    OUTPUT "Entries match"
  ELSE
    OUTPUT "Entries differ: check the intended identifier"
ENDIF

INPUT FirstEntry receives the first value. INPUT SecondEntry receives the confirmation. The condition uses = to test equality, not the assignment arrow.

On equality, output “Entries match”. On inequality, output a message asking for the intended data to be checked. The algorithm does not claim “Data is definitely correct”.

This fragment compares whatever text is supplied. Two empty strings also match, so a separate presence rule is needed if the data must not be blank.

09 | REPEAT WHEN THE ENTRIES DIFFER

A program can request two fresh entries after a mismatch and repeat the comparison until they agree.

DECLARE FirstEntry : STRING
DECLARE SecondEntry : STRING
REPEAT
    OUTPUT "Enter the identifier"
    INPUT FirstEntry
    OUTPUT "Enter it again independently"
    INPUT SecondEntry
    IF FirstEntry <> SecondEntry
      THEN
        OUTPUT "Entries differ: check and re-enter both"
    ENDIF
UNTIL FirstEntry = SecondEntry
OUTPUT "Entries match"

REPEAT runs the inputs before testing the final condition. UNTIL stops when FirstEntry equals SecondEntry.

If the first pair differs, the error message appears and the next repetition receives both values again. If they match, the loop finishes and the confirmation message is displayed.

This is a verification component, not a complete input routine. It still needs any required presence, format or other validation checks. It also does not consult an independent source to decide that a matching pair is correct.

A production form may let a user cancel rather than repeat indefinitely. The small algorithm focuses on the comparison and retry behaviour.

10 | TRACE TWO ATTEMPTS

On the first attempt, enter AB1402 and AB1042. The equality condition is false. The program outputs its mismatch message and repeats.

On the second attempt, enter AB1042 twice. The condition is true, so the loop ends and outputs “Entries match”.

Only the latest matching pair is accepted by this component. It does not combine characters from the earlier attempts or automatically choose which earlier entry was right.

If AB1402 were entered twice instead, the loop would also stop. That is why the message should accurately describe agreement rather than guarantee correctness.

11 | CHOOSE THE METHOD FOR THE TASK

When copying a small number of values from a readable paper form, a visual comparison can check the destination against that source directly.

When entering an intended address or newly chosen value without a separate source document, double entry provides a way to check whether the two entries agree.

For many records, visual checking takes attention and time. Double entry also adds input work and can still miss repeated identical mistakes. Neither method is automatically best in every situation.

Choose based on the available reference, the consequences of an error, the amount of data and how independently the entries or checks can be performed.

The methods can also be combined with validation. They address different reasons data may be unsuitable.

12 | VALIDATION AND VERIFICATION CAN COOPERATE

Return to a school mark from zero to fifty. Type and range validation can reject text or a value of 500. Verification against the paper can detect 43 copied instead of 34.

For an identifier, presence and format rules can check that something was supplied and follows the required pattern. Visual comparison or double entry can then reduce some entry mistakes.

Passing both does not prove every fact. A source could be wrong, a repeated error could match, or a valid identifier could have been intentionally selected for the wrong person.

Verification means checking entry or copying as intended; it is not another word for format checking. The next lesson compares validation and verification directly.

13 | TEST THE CHECKER’S ACTUAL CLAIM

For double entry, test identical values, different values, one empty entry and two empty entries. The last case reveals whether presence handling is separate from equality.

For our exact text comparison, AB1042 and ab1042 differ. A system can specify case normalisation before comparison, but that would change the rule and may be inappropriate for some data.

Leading or trailing spaces can also affect equality. Do not assume that a comparison trims them unless that behaviour is stated.

For visual checking, practise mismatched digits, transposed characters and correct values in the wrong record. Explain which source details must be compared to detect each discrepancy.

The expected outcome should describe the specific claim: entries match, entries differ, or entered data disagrees with its source.

14 | EXPLAIN THE METHODS WITH PRECISION

A clear description of visual checking is: “A person compares the entered data with the original source and corrects any detected differences.”

A clear description of double entry is: “The same intended data is entered twice and the computer compares the entries. A mismatch is flagged for correction or re-entry.”

For an explain question, include why the method helps and its limit: “Two independent entries can differ when one contains a typing error, therefore the comparison can flag the mistake. However, the same wrong value entered twice can still pass.”

Avoid saying that a mismatch identifies the correct entry or that agreement proves factual accuracy. You should now be able to apply both methods and describe exactly what their results establish.