What is another word for doing the top of head?
Pronunciation: [dˌuːɪŋ ðə tˈɒp ɒv hˈɛd] (IPA) 
The phrase "doing the top of head" can be replaced with several synonyms. One option is to use the phrase "off the cuff," which means to say or do something without prior preparation or thought. Another option is to use the phrase "from memory," which suggests that the action or statement is being done without the aid of reference materials or notes. A third option is to use the phrase "impromptu," which conveys a sense of spontaneity or improvisation. Whatever the synonym used, the implication is that the action or statement is being done without much forethought or planning.
