Many of the instruments used in early operations of the US Army Signal [Corps were adaptations of equipment used by the Plains Indians, particularly that of the heliograph].
Correct Answer: Corps, and in particular the heliograph were adpatations of quipment used by the Plains Indians.
My Answer: No Error
Is it because putting heliograph at the end makes it possibly describe heliograph as a type of Indian, or is there another reason?
Ms. Jordan proudly demonstrated her company's most popular product, a watch that flashes the time in lighted numerals when PRESSING A BUTTON. (capitalized is the error)
I got this correct but I need a concrete reason why this is an error.