This paper examines formant data from a corpus of male speakers of RP born during the twentieth century. It compares average formant positions in the F1/F2 plane for the short vowels LOT and FOOT. The relative positions of the two vowels are represented by a single numerical value, the calculated angle from LOT to FOOT relative to the vertical. Changing angle values between the early and the later part of the twentieth century can be clearly seen in the data, reflecting a diachronic process of FOOT-fronting well documented in varieties of British English, (Torgersen and Kerswill ), including RP, (Hawkins and Midgley ). One aim of the paper is methodological, in that it demonstrates the versatility of an angle calculation method developed by Anon , used in combination with F1/F2 plots, in producing replicable quantified measures which demonstrate changing vowel juxtapositions in real time.