1. Automatic -- The program selects
blocks at the start and/or end of the data and uses them in a regression
to compute the baseline. You can change the number of cases in these
blocks by editing the value in the box (the default is 15). Use the
automatic method only if the beginning and end
of the file contain nothing but true baseline values.
If this condition is not met, use another method (such as #2 or #3, below).
2. Automatic (periodic) -- The program uses one of three methods to identify baselines:
(a) The program uses markers in each reference as a cue
for baseline setting. You can chose which marker is the reference indicator,
and whether the reference adjustment should begin on either side of that
marker (and by how much). In my experience, this usually works more reliably than the second method and can deal with user-induced alterations in the reference vs. sampling schedule, but it does require markers at the appropriate points in the file. The LabHelper and Sable Systems acquisition programs will do that automatically, if properly set up.
(b) You use the cursor to select a starting point and time interval between
reference readings, and the program uses them to 'step' from reference
to reference. This method does not require any markers to indicate references, but it works well ONLY if all reference intervals in the file are exactly the same.
(c) You use the cursor to select a block, starting at the beginning of a reference point and lasting exactly as long as the interval between reference readings. Similar to method (b), the program uses the staring point and the interval (= block duration) to 'step' from reference
to reference. This method does not require any markers to indicate references, but it works well ONLY if all reference intervals in the file are exactly the same.
Only the first method (using markers) can be scripted.
3. Use the mouse to select a sequential series
of baseline blocks (multiple points), starting
from the 'left' end of the file and moving to the 'right' end. This
method corrects the baseline in a series of segments (up to 300 in a given
file; you can repeat the process if you need to handle more than that).
Alternately, you can click on single points (instead of selecting
blocks).
NOTE: you must select at least three blocks or points. For a one- or two-point correction, use the next options.
4. Use the mouse to select beginning and ending
blocks, which LabAnalyst then
uses in a linear regression to compute the baseline. Alternately,
you can click the single point button to pick baseline points (instead
of selecting blocks).
5. Use the mouse to select a single
block which the program uses to calculate a flat baseline. Alternately,
you can click on a single point (instead of selecting a block).
6. Keyboard entry of beginning and ending
baseline values.
7. Keyboard entry of a constant baseline value.
For all methods except #2 (automatic periodic references) or #3 (multiple
blocks), the baseline is drawn on-screen (if it fits within the current
Y-axis scale) and you can cancel, reselect, or accept it. The final
baseline is drawn across the entire file.