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A reference designator pins a build requirement to a specific location in the assembly, such as R7 or U3. See Bills of materials overview for how designators sit on the line. When a build requirement has reference designators, operators install per designator rather than satisfying a count, and ION treats a requirement with no designators as quantity-only.

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Configuring reference designators

On the build requirement’s row in the mBOM card, with the version in Draft:
  1. Open the Reference Designators dropdown in the row.
  2. Type a designator and press Enter (or click Add). Repeat for each position, for example R1, R2, through R12.
  3. To remove one, click the trash icon next to it in the dropdown.
Keep the number of designators aligned with the quantity, one per position. Each designator is unique within the build requirement. Two build requirements on the same assembly can both have an R7, but within one build requirement R7 appears once. ION doesn’t enforce a designator format.
Include reference designators when there’s a chance you’ll need positional traceability. Adding them later requires reinstalling every affected unit.
Don’t use reference designators for sequential count tracking. A torque pattern that needs fastener 1, then fastener 2, then fastener 3 is a procedure-step concern, not a designator.

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How operators install with reference designators

At run time:
  1. For each designator, the operator selects (or scans) the part inventory to install at that position.
  2. ION records the (designator, installed part inventory) pair on the aBOM.
  3. The build requirement is satisfied when every designator has an installation.
Operators can install in any order, because designators don’t impose sequencing. If the assembly’s procedure has a specific order, that’s enforced at the procedure-step level. In a run step’s Part installs panel, a designator that reaches the run step through an installation rather than an assignment is marked not assigned to this step. Assign it to the run step to have it count toward the assigned progress.

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Manage a designator’s run step

Assigning a designator to a run step claims it for that step, so the operator working the step knows which positions belong to them. One dropdown assigns, removes, and moves. Reach it in the Part Installs (aBOM) dialog:
  1. In the run, open the Part Installs (aBOM) dialog: on a run step, click View all in the Part installs panel of the right rail.
  2. Turn on Edit Mode.
  3. On the build requirement’s row, open the Reference Designators control.
  4. On the designator’s row, open its step dropdown.
  5. Pick a step. Picking an unheld step assigns or moves the designator to it; picking the row that already holds it removes it.
A run step’s row carries a marker when picking it would do more than a plain assignment:

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What a move does

There is no single operation that moves a designator, so ION removes it from its current step and assigns it to the new one. Both ends are redline-gated, so the confirmation names each run step whose approved redline will be cleared, one or two, and nothing is cleared until you confirm the whole move. An approval that lands after that confirmation stops the move rather than being overwritten.
The removal and the assignment are separate, so a move can fail after the removal has already succeeded, leaving the designator on no step. ION says so when it happens: an error appears, followed by a Move incomplete message naming the step the designator left and the step it did not reach. Reassign it from the same dropdown, which is back in its unassigned state.
A designator marks one physical position, so ION refuses to assign one that another run step already holds. That refusal is why a move is two writes rather than one. The same rule applies when a redline is canceled: if the designator has since moved to another run step, ION refuses the cancel rather than restoring the designator onto two steps. A run cut or an import can still land the same designator on two run steps. The dropdown shows both holders rather than picking one: each reads Assigned and is removable on its own step’s redline, and every other step reads remove from a step first until the designator is down to one. Deleting a designator removes its run-step assignment along with it, and the delete confirmation names the step that loses the assignment.

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Substitutes and reference designators

Substitutes are configured at the build-requirement level, not per designator, so an approved substitute applies to every position the requirement covers. At install time, for each designator the operator can install the primary or any approved substitute, independently per position. So R1 can take the primary while R3 takes a substitute, and the aBOM records which part went into which position. Because substitutes can’t be scoped to individual designators, if R3 and R7 need different alternates, make them different build requirements.