What is the first step in the alterations flow for handling fittings?

The first step in the alterations flow for handling fittings is measuring and pinning the garment. This step is crucial because it establishes the correct fit and allows for any necessary adjustments to be visualized on the actual garment. By measuring, the tailor can gather precise dimensions, which are essential for ensuring that the final fit meets the customer's requirements. Pinning the garment during this phase is equally important, as it helps to temporarily hold the fabric in place so that the tailor can assess how the alterations will look before making any permanent changes.

Addressing the other choices, while ironing the garment can be important for a neat presentation and accurate fitting, it is not the initial step in the alterations process. Checking the alterations request form would come before any physical adjustments to ensure clarity on the customer's needs, but it does not lay the groundwork for the actual fitting. Cutting along the marked line is a later stage that occurs after determining how the garment needs to fit, so it cannot come before measuring and pinning.