In a T&M contract dispute, the single most important documentation supporting the contractor's invoices is usually:

Explanation

A time-and-materials contract prices the work by inputs, so an invoice is worth exactly what the record behind it is worth: dated daily logs of who worked and for how many hours at which agreed rate, what material arrived, and the supplier invoices proving it. B&P §7159.10(e)(7) shows the same logic in statute for a service-and-repair job estimated on time and materials — the contract must disclose the set rate, the estimated cost of materials, and how time is computed, in quarter hours, half hours or hours. (a) is irrelevant to proving work done; liquidated damages fix the consequence of a breach in advance. (d) proves a precondition to suing at all under B&P §7031, not the amount owed. (b) documents attendance, not hours, rates, or materials.