# Duplicate validity

> last-split, wrong batch/lab/method void a pair

Source: https://geodb.io/guide/topic/qaqc_duplicate_validity/ · Category: QAQC
A duplicate only measures what it repeats. Break the repeatability
conditions and the pair silently stops measuring precision at all —
Simón's list of practices that void a duplicate:

- different crews, sampling methods, or intervals; long time gaps;
- taking the duplicate from the **last** split instead of the first;
- not inserting the duplicate **in the same batch** as the original;
- a different **analytical method, aliquot size, or detection limit**;
- sending original and duplicate to **different labs** (that's a check
  assay, a different tool);
- **relabelling coarse-reject re-pulps as "pulp duplicates"** — that
  converts an analytical-precision measure into a sub-sampling measure
  without telling anyone;
- inserting only one duplicate type — pulp-only makes field and
  sub-sampling error invisible.

One genuinely contested point: field duplicates from **quarter core**.
Simón describes it as the standard workaround; Bishi calls it "not
recommended… biased sampling." Know which side your project's protocol
takes.

## In geoDB

geoDB records each duplicate's **type** (field/coarse/pulp/lab) and links
it to its parent sample — the type decides which tolerance it is judged
against, so **log the type truthfully**: a coarse-reject re-pulp is a
coarse duplicate, not a pulp duplicate, even though it arrives as a pulp.
geoDB does not (and largely cannot) verify the field-side conditions —
same batch, same method, first split — those live in your sampling
protocol.