Fit first, output second — externally regulated only. Pick the engine and the tool loads the verified Whatcom crossover: the OEM number, the Whatcom stock unit, the belt/pulley type, and the external-regulator crossover to order (Whatcom ext-reg, then Balmar with a WS500). Belt/pulley is matched from real Whatcom data; foot-width and pulley-offset stay a verify-on-the-unit gate so you stop paying for returns.
Fit is decided by the alternator on the engine now — its mount, belt plane and ground — not the engine name or the amps. Start from the engine (loads the verified Whatcom data), or measure the unit.
Measure mode records the fingerprint and points you to the closest family — then confirm by running the tag’s OEM number through Whatcom OE Look-Up.
Saved on this device. Export CSV to grow the fitment library — every verified unit sharpens the next match.