N.H. Rev. Stat. Ann. § 564:2-c

The public trustee may establish common trust funds, in which may be combined money and property belonging to the various trusts in his care, for the purpose of facilitating investments, providing diversification and obtaining reasonable income; and provided, further, that the participating interests of said trusts are properly evidenced by appropriate bookkeeping entries showing on an annual basis the contribution, the profits, the income, the expenses, the fees and withdrawals allocable to each trust.