Green’s Dictionary of Slang

to appraise, to assess.

1894		Westminster Gazette 15 Feb. 5/1: The Liberal delegates were fervid only when ‘weighing-up’ the House of Peers and insisting upon its disestablishment.
1904		Daily Chronicle 14 Jan. 7: ‘I knew too much about her,’ she said. ‘I had weighed her up.’.
1938		D. Runyon ‘Dancing Dan’s Christmas’ in Runyon on Broadway (1954) 257: He weighs up the joint in one quick peek.
1938		J. Curtis They Drive by Night 102: Garn. You’re sprucing. You got me figured out and weighed up.
1958		A. Sillitoe Sat. Night and Sun. Morning 35: Though everybody might have the ability to weigh-up others, it never occurred to them to attempt a weighing-up of themselves.
1960		Wodehouse Jeeves in the Offing 38: ‘Or don’t you think so?’ I weighed this.
1985		S. Berkoff West in Decadence and Other Plays (1985) 123: I sense him now weighing up the scales of chance.
1999		K. Sampson Powder 348: He could just refuse to open up. [...] Or he could let her in and succumb to sex again. There was nothing to weigh up. He could not let that woman past the door.