Green’s Dictionary of Slang

(orig. Aus./N.Z.) the facts, the details of a situation; usu. as the strength of; thus get the strength of v., to understand.

1876		Aris’s Birmingham Gaz. 8 July 8/1: Hadley said, ‘That’s the place for you [...] (pointing to a lodging house). ‘That’s about your strength; you can have a “kip” for 3d’.
1894		Truth (Sydney) 14 Jan. 6/7: I left him [...] once more asking him if he had been skiteing or telling me the full strength.
1901		W.A. Sun. Times (Perth) 15 Oct. 1/1: Having got the ‘strength’ of the next-door neighbors boarders he tendered for their custom at a lower rate.
1908		Bulletin (Sydney) 16 July 14/2: Snorter sees the strength o’ ther game too late. ’E never got a chance ter land Bluey, who hung on his rear pants while Gingertop put his face through the stampers.
1914		E. Dyson Spats’ Fact’ry (1922) 38: The strength iv it is this [...] yous women hate men so much.
1919		W.H. Downing Digger Dialects 26: get the strength (or strong) of — Become possessed of sufficient information to enable one to form a correct judgement in regard to the matter in question.
1924		C.J. Dennis ‘A Holy War’ in Rose of Spadgers 41: I got the stren’th uv it in Spadgers Lane / Not ’arf an hour before’and.
1930		‘Leslie Charteris’ Enter the Saint 165: ‘You’re beginning to feel that you can’t go through with the job. Am I right?’ Tremayne spread out his hands. ‘That’s about the strength of it.’.
1938		X. Herbert Capricornia (1939) 371: Now come on, what’s the strength of this?
1944		A. Marshall These Are My People (1957) 142: You’ve been a shearer’s cook. What’s the strength of it?
1955		D. Niland Shiralee 44: What’s the strength of all this trouble they’re having with cooks.
1958		F. Norman Bang To Rights 10: When we got swaged into the meatwagon I asked another geezer the strength of him.
1962		R. Cook Crust on its Uppers 118: What’s the strength with these Gooch people.
1969		A. Buzo Rooted III iv: gary : I’m sorry, mate, but I’ve got to get with the strength. richard : You’ve got to be where the action is.
1976		D. Ireland Glass Canoe (1982) 156: What’s all this? [...] Come on, what’s the strength of you mob? What am I doin’ here?
1983		A. Payne ‘Get Daley!’ Minder [TV script] 39: A quiet bloke who liked a bet and was always a bit skint. That’s the full strength.
1986		R.G. Barrett Godson 20: ‘What’s the strength of dragging me away from my nice, warm, illegal casino’.
1988		McGill Dict. of Kiwi Sl. 108/2: strength of it, the reliable information or the extent of something under discussion, often as that’s about the strength of it.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].
2005		P. Temple Broken Shore (2007) [ebook] Yeah, well, that’s probably the strength of it. Mark me for a dog straight off.