Card Centering Calculator

---
name: card-centering-calculator
description: Works out a trading card's or sports card's centering from border measurements (millimetres, inches or pixels from a scan), front and back, and shows the best grade centering alone allows under each grader's published limits. PSA and CGC figures are bundled with their source and check date; BGS and SGC can be filled in. Flags borderline results that a re-measure could change, and handles one card or a batch from a CSV. Use when the user says things like "check the centering on this card", "is this 55/45", "what's the centering", "will this card get a 10 on centering", "measure centering before I submit to PSA", "is this off-center", or gives border widths or a scan to measure before grading or buying.
---

# Card Centering Calculator

Turn border measurements into centering ratios and say what grade centering alone allows. Be honest about what that means: centering is one factor, and graders use judgment.

Rules you never break:

1. **Centering only.** Never predict a final grade. Say "centering alone allows up to X". Corners, edges, surface and eye appeal can still bring the grade down.
2. **Only published limits.** Use the figures in `assets/centering-standards.json`, which carry a source and a check date. Never fill in a grader's limits from memory. BGS and SGC ship empty on purpose. If the user wants them, ask them to copy the figures from the grader's page (link in the file) and add them.
3. **Measurements come from the user.** If you measure from an image yourself, say how and how precise it is, and ask the user to confirm on the physical card for anything borderline.

## Bundled files

| File | When to use it |
|---|---|
| `scripts/centering.mjs` | Step 3. Prints ratios and the best grade per grader. Read-only unless `--out`, which never overwrites. Needs Node.js 18+. |
| `assets/centering-standards.json` | PSA and CGC limits checked on 2026-10-29, with BGS and SGC to fill in. The user can edit or copy it. |
| `references/measuring-guide.md` | Step 2. How to measure with a ruler, calipers or a scan, borderless and full-art cards, and common errors. |
| `examples/` | Six sample cards in mm and pixels, the batch report, a walk-through and test runs. |

## Step 1: What does the user want?

- **One card, quick check:** they give four border widths for the front, and ideally the back too.
- **A stack before a grading submission:** a CSV, one row per card. Offer to build the CSV from their notes.
- **A listing or a purchase:** they want to know whether a card in a photo is off-centre. Explain that photos can be skewed, and measure carefully or ask for a straight scan.

Ask which graders they care about. The default is every grader with figures filled in.

## Step 2: Get the measurements

Read `references/measuring-guide.md` if the user hasn't measured before, and walk them through it briefly:

- Measure the left, right, top and bottom border at the middle of each edge, in the same unit.
- On borderless or full-art cards, measure to the edge of a printed frame or design line that should be even. Say which reference they used.
- Measure the back too. Many graders allow wider back tolerances, but a badly centered back still limits the grade.

If the user gives an image and you can view it, you may estimate pixel distances, but:
- say they're estimates from the image;
- state that lens angle and cropping distort them;
- recommend a flat scan at 600 dpi or more for anything near a limit.

## Step 3: Run the calculator

One card:

```
node <skill-folder>/scripts/centering.mjs --front L,R,T,B --back L,R,T,B --card "<name>"
```

A batch (columns `card, front_left, front_right, front_top, front_bottom, back_left, back_right, back_top, back_bottom`; back columns may be blank):

```
node <skill-folder>/scripts/centering.mjs --csv <measurements.csv> [--out <report.md>]
```

`--graders psa` limits the graders. `--standards <file>` uses the user's own edited copy.

Without Node.js: work it out by hand. For each pair, ratio = larger ÷ (left + right) × 100. Take the worse of left/right and top/bottom, and compare it with each grade's limit, best grade first. Say the script wasn't run.

## Step 4: Report back

Keep it short, in this order:

1. **Ratios.** Front left/right and top/bottom, back the same, with the worst axis. Say which way the image is shifted, from the report.
2. **Best grade centering alone allows**, per grader, copied from the report, with each note:
   - "borderline: re-measure" when a better grade was missed by 2 points or less;
   - "within X of the limit" when it barely passed;
   - "back not measured" when only the front was given.
3. **What it means.** For example: "On centering alone this can still be a PSA 10, but only just. Corners, edges and surface will decide the rest." For a stack, list which cards are worth submitting on centering and which aren't.
4. **The standards used.** Grader, source page and check date, from the report. Mention that graders can change their standards, and that PSA says it may allow a small variance for eye appeal.
5. Any grader the user asked about that has no figures filled in, and how to add them.

## Rules

- Never say a card "will grade" anything. Use "centering alone allows".
- Don't round a ratio to make it pass. Report it to one decimal.
- If the user's numbers look implausible (one border 10 times another, or a border wider than about 8 mm on a standard card), ask them to re-check before running.
- If the user is buying a card, add that centering can be judged from a scan, but corners, edges and surface need closer photos or the card in hand.