NavList:

Mike you wrote:

In my earlier post I indicated I only had 1 page of AP3270 Vol 3 in my book (Mary Blewitt) for reference. I thought the tiny - signs against the d values were intended to be minus signs. Additional evidence by inspection of the data revealed as the declination increases from 15 to 29 degrees the Hc reduces.

It depends where you open the book, i.e. your latitude and if declination name (N or S) is the same or opposite.  E.g. lat 50N, dec 20N and increasing, Moon coming towards you, so Hc increasing.  Lat 50N, dec 20S and increasing, Moon going away from you, so Hc decreasing.  But, Lat 10N (Vol 2), dec 20N (i.e. lat less than dec) and dec increasing, Moon travelling away from you, so Hc decreasing.

You also wrote:

I have downloaded AP3270 Vol 2 & 3 and note that when Hc increases in line with an increase in declination no sign is given against d values  (no + sign). Assume to be additive unless otherwise indicated.  Is this a reasonable observation.

It depends which edition of Vol 2 & 3 you look in.  The latitude pages of the latest on-line editions of  Vols 2 & 3 have nothing in front of ‘add’ d s  and – in front of every ‘subtract’ d, but my 1960s hard-back copies have a + in front of ‘add’ d s in a column when the LHA is divisible by five and a – in front of ‘subtract’ d s when the LHA is divisible by five, possibly to avoid printing ink clutter.

It’s worth buying second hand hard-back copies of Vols 2 & 3, because they're inexpensive, last for ever, and are easier (IMHO) to find your way around than the on-line versions, but a second hand Vol 1 is less valuable, because it’s epoched and is of little use outside its 10 year epoch. DaveP