Ephemeris data mismatch between Nasa Horizonz and Astro.com I have tried to compare the Ephemeris data from Nasa's Horizons with ephemeris 
tables from astro.com. And they do not match. Example:

Date: 22th of July 2018. Body: Mars. Time 00:00 UT
Horizons: 309 degrees (Ephemeris type=Observer)
Astro.com: 305 degrees (http://www.astro.com/swisseph/ae/2000/ae_2018.pdf)

But some bodies are matching. Like Mercury and Saturn. 

Am I doing something wrong?

Sources:
Nasa Horizons: https://ssd.jpl.nasa.gov/horizons.cgi#top

Astro.com: http://www.astro.com/swisseph/swepha_e.htm
You might be comparing an ecliptic longitude to a right ascension.
These are measured around different circles, the ecliptic and the equator respectively.
Their values coincide at the solstices ($\lambda$ 90$^\circ$ or 270$^\circ$, RA 6h or 18h) but generally not elsewhere.

With target body Mars, a geocentric observer location, and output quantities 2 (apparent RA &amp; Dec) and 31 (observer ecliptic lon &amp; lat) selected, JPL HORIZONS gives:

Date__(UT)__HR:MN     R.A.__(a-apparent)__DEC    ObsEcLon    ObsEcLat
2018-Jul-22 00:00     20 38 23.96 -24 58 44.6 305.5424192  -6.2964464


RA 20h 38m 24s is 309.60$^\circ$, but the quantity to compare is the ecliptic longitude, 305.54$^\circ$.

The Astrodienst ephemeris table, based on JPL DE431, gives ♒ 5$^\circ$ 33', i.e. ecliptic longitude 300$^\circ$ + 5.55$^\circ$ = 305.55$^\circ$, for Mars on 2018-07-22.