For EHRs, blockchain might be able to store things that happen to you on a doctor’s visit (blood work, a new prescription, maybe some X-rays). Then people validate the transactions—in health care, likely a physician or pharmacist trusted with an access key. Then the software timestamps each validated block and adds it to a chain of older blocks, in chronological order. The sequence shows every transaction made in the history of that ledger, whether it be bitcoin sales or a knee replacement procedure.