At Copan a combination of a long count date and the visibility of Venus in relation to the alignment of Temple 22 and Stela 10 can be used to test specific Ahaw coefficients. On Stela 10 the Initial Series date is 9.10.19.13.0 3 Ahaw 8 Yaxk'in. The other data on this monument is 9.11.0.0.0 12 Ahaw 8 Keh which falls 100 days later than the Initial Series date and is most likely the dedication date of this monument.
Stela 10 was also visible through a narrow window (width 16-20 cm, length 220 cm) in Temple 22, the axis of which is 8°25' North of West (Aveni 1980:246). This temple is called the Venus temple because it is decorated with three 'star' or Venus signs at the entrance.
The long count date 9.11.0.0.0 is 18x584+328 days after the base of the Venus Table (9.9.9.16.0). This means, that 9.11.0.0.0 is only two days after the Venus station 10 Etz'nab 6 Keh of the Venus table (page 50) and therefore Venus should be near its first visibility as evening star about 8° North of West, above the horizon, and 328+4 = 332 days after the inferior conjunction. It is necessary to use a correlation to determine the visibility of Venus on this day. The arcus visionis is 5°48' as given by Schoch (1924:734) for the first visibility of Venus as evening star. This minimum necessary vertical distance between the Sun and Venus is reached if the sun is 5°48' below the horizon.
In the GMT-correlation (584285) 9.11.0.0.0 is 11 Oct. 652 Julian. The Venus station on this date was 317.6 days instead of 332 days after the inferior conjunction. The sun was at an altitude of -5°40' (i.e. under the horizon), the altitude of Venus was +1°07' and the azimuth was 11°29' South of West. On this date (11 Oct. 652 Julian) Venus was not visible in the window of Temple 22.
In the WF-correlation (660208) 9.11.0.0.0 is 23 Aug. 860 Julian. The Venus station was 333.5 days instead of 332 days after the inferior conjunction. On this date the Sun was at an altitude of -5°43' (below the horizon), the altitude of Venus was +4°03' and the azimuth was 5°51' North of West. Venus was visible as evening star through the window of Temple 22 and it set directly behind Stela 10. In the WF correlation 9.11.0.0.0 is 23 Aug. 860 Julian. The Venus station was 333.5 days instead of 332 days after the inferior conjunction. On this date the Sun was at an altitude of -5°43' (below the horizon), the altitude of Venus was +4°03' and the azimuth was 5°51' North of West. Venus was visible as evening star through the window of Temple 22 and it set directly behind Stela 10.