Face Dipstick 2277 - How To Determine Data Collection Bias Using An Out-And-Back Run

CHAPTER 9 - BIAS
9-5
How To Determine Data Collection Bias Using An "Out-And-Back" Run
To determine Bias, the Dipstick must be walked in
a closed loop, where the first reading and the last
reading finish on the exact same spot. This can be
a box, circle or straight line.
Here’s how to do it using an “Out and Back” Run:
 The surface must be uniformly clean and have
no obstructions on it.
 Mark a line ~50 feet long down the surface.
 At one end of the chalk line, carefully mark a
starting point using the crayon provided in the
Dipstick Kit.
 Assemble and zero the Dipstick.
 Start a new run.
 Place the Battery end foot of the Dipstick on
the starting point of the line and begin
collecting data, walking the Dipstick along the
line.
 After the Dipstick beeps at the ~50 foot (15 m)
mark and a reading is taken, pick up one end
and set it back down in exactly the same place,
then collect a second reading in exactly the
same place.
 Continue taking readings going back down the
same chalk line in the opposite direction.
Rotate the Dipstick back to the starting point to
take the final reading.
 Be sure to take the final reading exactly on
the original starting point.
 Tap “STOP” at the end of the run.
 This will produce an Elevation Graph and the
IRI for the run (if 37 or more steps have been
collected). Tap the “Close” box to clear the
graph.
 Use CALCULATE/BIAS.
Remember, the normal way to deal with Bias is to collect the data in “Boxes”.