GMN Check Character Calculator

How GMN Check Character Calculator Works?

The GMN Check Character Calculator works by converting each character of a Global Model Number (GMN) to a value in the 82-character GS1 set, multiplying by prime weights, reducing the sum modulo 1021, and writing the result as 2 characters from a 32-character set.

1. 1Convert each GMN character to its value in GS1 character set 82 (CSET 82).
2. 2Give the rightmost character the weight 2 and step up through the prime numbers 3, 5, 7, 11… moving left.
3. 3Multiply each value by its weight and add the products.
4. 4Reduce the sum modulo 1021 to get a value 0–1020.
5. 5Split the value into 2 parts of 5 bits each and map each part to CSET 32 (23456789ABCDEFGHJKLMNPQRSTUVWXYZ).

GMN Check Character Calculator Formula

The GMN formula is V = (Σ v(cᵢ) × pᵢ) mod 1021, with check characters CSET32[⌊V / 32⌋] and CSET32[V mod 32].

V = (Σ v(cᵢ) × pᵢ) mod 1021,  pᵢ = i-th prime counted from the right (2, 3, 5, 7…)
Check 1 = CSET32[V >> 5]
Check 2 = CSET32[V & 31]

• v(c) is the CSET 82 value of character c.
• pᵢ is the prime weight.
• CSET32 is the 32-character output set without 0, 1, I, and O.

Weighted sum mod 1021 = 17
17 >> 5 = 0 → 2
17 & 31 = 17 → K
Check characters = 2K
GMN = (8013) 1987654Ad4X4bL5ttr2310c2K

GMN Check Character Calculator Conversion Table

The GMN conversion table shows sample model numbers with their 2 check characters and the CSET 32 output range.

CSET 32 maps values 0–31 to 2–9 and A–Z without I and O, so check characters never contain 0, 1, I, or O.

What is GMN Check Character Calculator?

A GMN Check Character Calculator is a tool that computes the 2 check characters at the end of a Global Model Number. A GMN identifies a product model or design, and GS1 uses the GMN as the Basic UDI-DI for medical devices under the EU Medical Device Regulation (MDR).

A GMN holds up to 30 characters, including the 2 check characters, and is encoded with Application Identifier (8013). The 2 check characters give 1,021 possible check values instead of the 10 values of a single digit.

What are the uses of GMN Check Character Calculator?

There are 3 main uses of the GMN Check Character Calculator, including Basic UDI-DI numbers, model registers, and product data checks.

• Basic UDI-DI: Medical device makers register GMN-based Basic UDI-DI values in the EUDAMED database.
• Model registers: Manufacturers identify product models across product generations.
• Product data checks: Data pools reject GMNs with wrong check characters.