For Information Purposes - Please do not shoot the messenger
In "Sex and the Outer Planets" Barbara Watters gives the formula used for casting the Johndro charts which give primary consideration to the place of birth or residence rather than the time of birth.
In Johndro's book "The Earth in the Heavens" he gives an explanation on the precessional factor for RA. He uses Greenwich but states that the coincidence of Greenwich with the vernal equinox actually happened in 365BC so the first calculation rectifies this.
The annual rate is 46.10 seconds per year (not 50.25 seconds as it is on the ecliptic).
Taking (his chosen year) 1930 figure of 29 degrees 10 minutes you multiply the number of years before or after 1930 by the annual rate and subtract or add the result to get the RAMC for Greenwich for the desired year.
Then taking the latitude of the birthplace you add for East, subtract for West (and add 360 degrees if the longitude to be subtracted is greater than the RAMC in Greenwich which it will be for the USA).
This gives the RAMC for the desired location.
Now, take the position of the Sun for the date of birth in the correct year from your ephemeris.
Enter a table of RA to discover the RA of the sun for that degree.
Add this factor to you previous sum.
This gives the RAMC for the place and date of birth.
With a table of Houses for the appropriate latitude of the birth place use this RAMC to establish the cusps of houses.
If the birth hour is known figure out the correct positions of the planets and place within the Johndro locality chart
Otherwise enter the planets as shown in the ephemeris for noon or midnight GMT as the case may be (!)
Note on the chart the hour this would be at the location
eg if using a noon ephemeris the hour in NYC for the given planetary positions would be 7am, with a midnight ephemeris it would be 7pm
Barbara then works an example using the USA 1776 chart.
Johndro's book - which I got in a second hand bookshop in Glasgow, Scotland - has a useful table of cities of the world and their latitudes, RAMC's, midheaven's and ascendants.
Sarah