Here's the latest framework from Claude: We measure each card's exact carbon footprint from its Etherscan gas receipts — PoW-era transfers at CCRI's 25.1 kg/tx, PoS-era gas at 11 µg/unit, with lifecycle multipliers (2×/10×) for hardware and infrastructure. Registering a card swaps your ETH into CHAR (Toucan's biochar token, 1 CHAR = 1 tonne of Puro.earth-certified carbon removal) and the contract retires it in Puro's registry, whole tonnes at a time, entirely onchain. The only trusted input is the gas data itself, posted by allowlisted wallets and locked once written — everything else is contract code anyone can verify. A typical card costs ~$3 to cover (#461: 15.4 kg). Cards with PoW history run much higher (#1: ~339 tonnes). Every number is recomputable by anyone from public data. Contract is built and fully tested on Base; #461 registers first. No servers anywhere. Concerns The gas data is attested, not chain-verified. The EVM can't read transaction history on any chain, so someone has to carry Etherscan data onchain. We use allowlisted wallets with write-once data; anyone can audit a number against Etherscan, but the contract itself can't catch a bad submission before it's locked. The multipliers are judgment calls. 2× PoW / 10× PoS lifecycle is our order-of-magnitude estimate for everything beyond validator electricity. Reasonable people will disagree in both directions. Retirement is batched, not instant. Puro only retires whole tonnes, so small registrations pool CHAR in the contract until a tonne accumulates — your card is "covered" immediately but the retirement certificate lands later, and that step is owner-triggered. Onchain carbon liquidity is thin. The CHAR/USDC pool holds ~$25k. Fine for $3 cards; the big PoW-era cards (hundreds of tonnes) exceed all onchain removal liquidity and would need offchain purchase.