A second display can keep source records beside a calculation, but visibility is not the same as traceability. When a worksheet contains many similar rows, it is easy to read a value from the wrong record and enter it into the active formula. Build the layout around stable identifiers and checks rather than relying on eye movement between two open windows.
Keep the record identity visible
Show the relevant row identifier, date or account code on both sides of the comparison. A row number can change after sorting or filtering, so use an actual record key where available. If one file has been sorted differently, matching the twenty-third visible row on each screen does not establish that the rows represent the same item.
Use appropriate freeze panes, table headers or pinned labels to preserve context while scrolling. The specific feature depends on the spreadsheet application, but its purpose is consistent: values should remain associated with their fields and records. An unlabeled number can look plausible even when it belongs to another period or unit.
Distinguish source cells from calculated results. If the task involves checking a formula, display the relevant expression or reference information as well as its output. A correct-looking total is not sufficient evidence if the formula includes an unintended range or excludes records hidden from immediate view.
Control copying and verification
Decide which workbook is the working file and which is a reference. Avoid editing the source accidentally because focus changes when the pointer moves to the other monitor. Where appropriate, use an authorized read-only reference view or clearly distinguish the files through names and window titles.
Test one known record independently before processing a larger set. Check identifiers, units and expected calculations by a suitable method, then change a controlled input if the task calls for validating the formula. The two-screen arrangement supports this work, but it does not replace the actual verification of references and arithmetic.
If the applications support a documented lookup or import process, consider whether that is more reliable than manual retyping. Automated transfer also needs checks for duplicate keys, missing matches and changed source formats. Do not assume that either manual visibility or automation is inherently accurate without testing the relevant failure cases.
Keep a short audit note for unresolved discrepancies, naming the record key and affected field rather than merely the screen position. At the end, verify saved output and the intended source relationship. A useful dual-screen layout preserves the context required to explain every selected value, allowing the person to follow the calculation without substituting visual proximity for reliable record matching.