Green’s Dictionary of Slang

anna n.

In phrases

[Hind. ??? (?n?) a coin (obs. since 1975) worth one sixteenth of a rupee] [X] annas in the rupee (adj.)

(Anglo-Ind.) with variant number, used to indicate a percentage of non-white parentage.

[Ind]G.W. Johnson The Stranger in India I 182: There are, of them, various shades, proportioned to their nearer approach to a purely white extraction; and to distinguish the gradual approximation, a whimsical nomenclature has been adopted. The offspring of a white father and coloured mother is said to be eight annas in the rupee. If this offspring has children by a white father, these are said to be twelve annas in the rupee!
[Ind]W.W. Knollys Misses and Matrimony 89: Nasty little black things; I am sure they are more than half niggers; twelve annas to the rupee, as Broughton used to say, for it was a very hot day, and I could see that their knuckles were quite blue. Aunt says you can always tell a half-caste in that way.
E. Braddon ‘Life in India’ in Fraser’s Mag. Sept. 339/1: The presence of Indian blood in any quantity may be detected easily enough, and the Anglo-Indian has no doubt about the Eurasian, of whom it is facetiously (if not good-naturedly) said, that he has a considerable touch of the tar brush about him, or a tolerable dash of coffee in his composition, or is four or six annas (i.e. four or six parts of black blood out of sixteen, there being sixteen annas in the rupee).
[Ind]G.R. Aberigh-Mackay Twenty-one Days in India 124: The convenient term quadroon, for instance, instead of ‘four annas in the rupee,’ is quite unknown.
[Ind]Yule & Burnell Hobson-Jobson 22/2: Anna. [...] The term is also sometimes applied colloquially to persons of mixt parentage. ‘Such an one has at least 2 annas of dark blood’ or ‘of coffee-colour.’ This may be compared with the Scotch expression that a person of deficient intellect ‘wants two-pence in the shilling’.
[UK]H.A. Giles Glossary of Reference on Subjects Connected with Far East (2 edn) 6: Eurasian are often spoken of as so many annas in the rupee, referring to the proportion of ‘dark’ blood in their veins. Thus, ‘four annas in the rupee’ would be equivalent of Quadroon.
[Ind]E. Thurston Castes and Tribes Sthn India II 229: The racial position of Eurasians, and the proportion of black blood in their veins, are commonly indicated, not by the terms mulatto, quadroon, octoroon, sambo (or zambo), etc., but in fractions of a rupee. The European pure breed being represented by Rs. 0-0-0, and the Native pure breed by 16 annas (= 1 rupee), the resultant cross is, by reference to colour and other tests, gauged as being half an anna in the rupee (faint admixture of black blood), approaching European types; eight annas (half and half); fifteen annas (predominant admixture of black blood), approaching Native types, etc.
[Ind](con. 1950s) C. Allen Plain Tales from the Raj 216: ‘When I was very young I took the conventional attitude which everybody took – even enlightened people like my parents – of making jokes about “blackie-whites” and “twelve annas in the rupee”’.
not sixteen annas to the rupee (adj.)

lacking in some quality, e.g. trustworthiness, honesty, intelligence [var. on not all there adj.].

[[Aus]‘A Week in Oxford’ in Bell’s Life in Sydney 25 Oct. 4/3: They [i.e. horses] have the right quantum of aristocratic blood, are three-quarters thorough, and as they say in the east, are twelve annas in the rupee].
[UK]Partridge DSUE (8th edn) 806: not sixteen annas to the rupee [...] ca. 1880–1940.
C. Hitchens in London Rev. Bks 26 Oct. 🌐 In neither world [i.e. India or the UK] is he considered to be quite sixteen annas to the rupee.
[UK]Taki’s Mag 17 Feb. 🌐 The old Raj-era expression ‘not quite sixteen annas to the rupee’ ( = ‘not playing with a full deck,’ ‘one brick short of a load,’ ‘smoke doesn’t go all the way up the chimney,’ ‘one coupon short of a toaster,’ etc., etc.) has fallen into obsolescence.
W. Keegan Guardian 12 July 🌐 A description from the adventure stories of my youth came to mind: ‘he is not quite 16 annas to the rupee’ was commonly used to describe someone you could not entirely trust.
[UK]J. Meades Empty Wigs (t/s) 186: Poor fellow appears to have been stupidly mean [...] Not quite sixteen annas to the rupee.