The ISO standard 22095:2020, on chain of custody models, defines book and claim alongside other models as follows:

3.1.1 — Chain of Custody — process by which inputs and outputs and associated information are transferred, monitored and controlled as they move through each step in the relevant supply chain

3.3 Chain of Custody models:

3.3.1 — Identity Preserved model — Chain of Custody model in which the materials or products originate from a single source and their specified characteristics are maintained throughout the supply chain

3.3.2 –Segregated model — Chain of Custody model in which specified characteristics of a material or product are maintained from the initial input to the final output. (Note: Addition of material with different characteristics and/or grade to the input is not allowed)

3.3.3 — Controlled Blending model — Chain of Custody model in which materials or products with a set of specified characteristics are mixed according to certain criteria with materials or products without that set of characteristics resulting in a known proportion of the specified characteristics in the final output. (Note: The adhered claim may refer to a certain percentage, at batch-level and /or site-level.

3.3.4 — Mass Balance model — Chain of Custody model in which materials or products with a set of specified characteristics are mixed according to defined criteria with materials or products without that set of characteristics. (Note: The proportion of the input with specified characteristics might only match the initial proportions on average and will typically vary across different outputs.)

3.3.5 — Book and Claim model — Chain of Custody model in which the administrative record flow is not necessarily connected to the physical flow of material or product throughout the supply chain. (Note: This Chain of Custody model is also referred to as ‘certificate trading model’ or ‘credit trading’.)