Posted because the precise measurements of body and horn length could be useful. "Body" means head to rear of last abdominal segment, not including any part of horn.

Measured with jeweler's calipers, which are subdivided to half a millimeter; after a lot of practice, I can actually touch the tips to a motionless insect without damaging it.

Plant: Tomato (Solanum lycopersicum). The caterpillar is probably a Carolina sphinx, considering its foodplant, but I'm waiting for another instar or two to make sure.