You need a PIC-controlled robot that roams randomly around
the free-range area. It would detect unwary chickens using
a combination of Laser, Radar, Heat Sensing, and Ultrasonic
Detection. Through the combination of detectors the robot can
differentiate between dead chickens and live chickens.

Once it has detected a live chicken within capture range,
it would advance and capture the chicken. The robot
would be equipped with a multitude of capture devices,
such as scoops, nets, suction hoses, and telescoping arms.
Once the chicken is captured it would be held tightly
so that it can't move at all. The robot would then become
very still and weigh itself and the chicken using
built-in strain gauges. Once this robot+chicken weighing
is finished, the robot would attach a PIC-controlled
electronic tag to the chicken, if it didn't already have
one attached. This tag would record the chicken's ID code,
and the date and time of this and all subsequent weighings
together with the weight recorded at each weighing session.

Since the initial weighing assumed that the chicken was
perfectly still, there is some chance for error in the
weighing if the chicken was still struggling.
So, upon release, a second form of weighing
would be employed. I call this method the ballistic method.
Since an object with mass has enertia, we would measure
this inertial value by hurling the chicken away from the
robot at a known velocity. This ballistic measurement
would then be converted into a standard weight value
by a PIC doing 32 bit floating point arithmetic.

Once the ballistic measurement phase is over, the robot
weighs itself using its built-in strain gauges, then
calculates its at-rest mass. A little math and it has
TWO measurements for the mass (and therefore weight)
of the chicken. It should be noted that such a measurement
system will work on the moon as readily as it works on
earth. You would, of course, have to calculate
different table values or multiply the answer by a
different constant to convert the mass to a weight
measurement.

An absolute mass value can be obtained if the chicken
is held tightly and vibrated up and down and along
different planes. Subtract the smallest reading from the
biggest reading to cancel out the effect of gravity.
If properly done the resultant mass reading will also
be the same as the readings obtained when the chicken
is vibrated parallel to the floor.

Please note that this ballistic measurement is somewhat
different from that proposed earlier by another PIC list
member who proposed measuring the IMPACT of a chicken
against the barn wall. MY proposal is to measure the
inertial value AT LAUNCH, *not* at IMPACT.

Hurling the chicken away from the robot also takes care of the
problem of the robot accidentally grabbing the same chicken
too often, as the chicken thus launched would now be many
yards away from the robot. My quick calculations show that
resolution of the inertial value for mass increases with
increasing velocity. So it is beneficial to hurl the
chicken away with as great a velocity as possible.

If the ID tags attached to the chickens are properly designed,
the robot could detect the time of last capture and
ignore any chicken that had been recently captured. This would
reduce the trauma experienced by any given chicken over
any given day. It does require the ID tag to be teamed up
with a small transmitter.

If a chicken is captured and determined to be under-average
weight, the robot could force-feed the chicken something
that weighs a lot, such as chicken feed mixed with gravel or
lead shot. This has the beneficial side effect of making
the chicken somewhat slower on it's feet. Thus the robot
will be able to capture it later on more easily.

If you really want to make life easier for the robot,
consider attaching a miniature electric shocking device
to each chicken when it is tagged. When the robot got
near it's victim it could initiate a massive electric
shock that would prevent the chicken from running away.

Since each ID tag is unique, the robot could search out
and incapacitate any chicken it wanted. If ALL tagged
chickens were simultaneously shocked so as to make them
fall over, the robot could then scan for any chickens
that were still standing. These would be the un-tagged
chickens. The robot could them target them especially
so that eventually all chickens that weren't dead or
otherwise incapacitated would be tagged.

I can really use that $1,000

Fr. Tom McGahee