A variation is any change to the work after the quote has been accepted. It can add work, such as extra power points or a second garden bed. It can take work away, such as a fan the customer no longer wants. It can swap one thing for another, such as a tile that is out of stock replaced with a dearer one. And it can come from what is found on site, such as rotten framing behind the old shower. Each one changes the price, the time or both, and each should be priced and agreed in writing before the changed work is done. A variation that reduces the price deserves the same paperwork as one that increases it.
Home building laws in some states require variations to domestic building work to be in writing and agreed before the work is carried out, and limit what can be charged for variations that were not. Your state's building regulator or fair trading office can tell you whether that applies to your work.
In practice
An electrician's accepted quote for a kitchen renovation is $2,350. Halfway through, the owner asks for three more double power points along the bench. The electrician prices them at the same rate as the originals, $165 each, sends a variation for $495, and waits for the yes before cutting in the boxes. A week later the owner drops one of the two pendant lights from the original scope, and the electrician sends a second variation crediting $180. The job finishes at $2,665, and every dollar of the difference from the original quote is on a dated, accepted document.
The habits that make variations painless: a sentence in the original quote saying changes are priced and agreed before they are done; the same pricing basis as the original, so the extra looks fair; and stopping before the extra work rather than explaining it afterwards. The guide to handling variations covers what to say on site.
In Quote Desk
Send each variation as a new quote from New quote on the Quotes page. The Quote this button on the customer's enquiry disappears once that enquiry has a quote, so later quotes for the same job always start from New quote. A negative line is not accepted, so a credit goes on as a zero-priced line that names the amount coming off. The original stays exactly as accepted, and each variation has its own accept and date; see quote statuses.