BJ write:

When a controller wants "speed", they are asking for the pilot's
INDICATED airspeed. Controller's can only see GROUND speed on their
radars.

When a controller asks for altitude, he/she is verifying the altitude

he/she sees on their radar with what the pilot is seeing on their
altimeter. It's a backup and safety thing so that there is no
confusion
and to verify the transponder is sending accurate information.


When a controller ask for heading, they are asking for the compass
heading the aircraft is flying. Controllers can only see the TRACK
the
aircraft is flying.

Also, it's safe to say that a percentage of time the controller is
asking these questions to prod the pilot to get back on the course
and/or altitude that the controller last assigned. :-)

--
Peter