Repeating parallel instructions

["Geoff Hart (by way of \"Eric J. Ray\" <ejray -at- raycomm -dot- com>)" <ght -at- MTL -dot- FERIC -dot- CA>]

Philip Sharman is <<writing a set of procedures to tell an installer
how to set up some equipment, which consists of two systems.  95% of
the steps for the two systems are identical, but there are some
differences.>>

If you're really talking about small differences between the two
systems, then it's much more effective to teach one overall approach,
with the two variants clearly identified in the few steps where
differences occur. This teaches the overall approach (conceptual and
procedural information) by example, and provides the specific
parameters that vary (reference information), and I find this
particularly effective because it teaches you a consistent way of
working with the system as well as where the exceptions to this
consistency lie. For example:

Step 17. Enter your name:
- In the Firstname module, enter your given name (e.g., Geoff)
- In the Lastname module, enter your family name (e.g,. Hart)

You can also do this effectively with a three-column table: Column 1
contains the instructions for each step, and columns 2 and 3
(respectively) represent any parameters that differ between the two
systems for that step. The same tabular approach adapts well to
all kinds of other situations; for example, a command reference
could use two columns: column 1 is the command, and column 2
lists the parameters. See the basic approach?

The real problem is that at some point, the two systems become
sufficiently different that you can't overlap their instructions. I
have no idea where that point lies, but I suspect that it occurs
(i) as soon as you can no longer simply list the two options as I've
done above and (ii) at a different place for every type of
description (in some cases at 50% similarity, in some cases at 75%).
For example:

Step 18. From here on, the two systems differ enough that you need
entirely different instructions:
- To complete the Firstname module, turn to page 20
- To complete the Lastname module, turn to page 40.

You can use a binary approach ("if yes, then go to step 19; if
not, go to step 27"), but this can be confusing. I've also seen
flowcharts used in cases like this, but I often find them difficult
to use for long, complex procedures (i.e., it's easy to lose your
place in the chart and have to start over again). Although this may
simply be a function of poor flowchart design, I suspect there's a
more fundamental cognitive principle going on here.
--Geoff Hart @8^{)}
geoff-h -at- mtl -dot- feric -dot- ca

When an idea is wanting, a word can always be found to take its place.--Johann Wolfgang von Goethe

 From ??? -at- ??? Sun Jan 00 00:00:00 0000=