A complete change order includes: a sequential change order number for tracking; the date issued; the project and contract reference; a specific scope description (what work is being added, removed, or modified, specific enough that both parties reading it independently would understand the same thing); the cost impact — lump sum or T&M with labor and material broken out separately; the overhead-and-profit markup at the contracted rate; the schedule impact in calendar days; the reason for the change; the updated contract total (original plus previous COs plus this CO); and both party signatures. Missing any element makes the change order incomplete and its enforceability weaker. The running contract total update is particularly important — without it, the client cannot track the current authorized project cost.