Several points here, Barry:
First, Tiny Tach makes several different models, but as you said it only pays
attention to one cylinder. However, if I'm not mistaken they make models for
engines which fire twice per revolution, once per revolution and once every
other revolution. They also have some sort of provision for a three-cylinder
which has some sort of odd timing issue.
My biggest argument here though is about analog tachs. IMHO, an analog gauge
is far more useful to a human during normal operations than a digital gauge.
"Right next to the red" is more useful and more intuitively understood than
3573, since you have to remember what the max is, then compare that number to
what you see moving around on your tiny tach. This is even more of a problem if
you have two tiny tachs, one which redlines at 3600 and one that redlines at
6800. This might be a slight inconvenience when you're going 30 mph going down
a river, but in the middle of a race or when you're cruising at 60+ mph it can
be a real pain.
You have a point about accuracy with analog gauges though, and you may remember
my earlier queries about digital sensors with an analog gauge. Some cars use
them, the computer makes a reading from the sensor, then moves the gauge. I've
seen the calibration process on a BMW, all the gauges sweep slowly left to
right, all at the same angle and in sync.
In all reality, for most systems an analog gauge can be every bit as accurate as
a digital one. Especially since even the digital gauge relies on an analog
sensor in most cases. RPM is one of the few things that can be measured
directly by counting something. Human interfacing is an often neglected but
critically important part of design. A prime example is probably just on the
right edge of the window you're reading this message in. It would be more
accurate to have a digital readout of what line you're on at the top of the
window and what line on the bottom, and a small text box to type in which line
you want to scroll to, but instead they have a little bar with a slide on it,
and you drag it with your mouse. I'm not sure if that idea came from Apple or
Xerox Park, but lots of people can't do business without it and few people think
of how much trouble it saved them.
Post by s***@aol.comThe Vanguard 18 fires on every revolution. Remember, the "Tiny Tach"
is used on only one cylinder, so use on one or two cylinder engines is
the same.
Analogue tachs, well, for lack of a better description, are purchased
for decoration of vehicles, except for competition vehicles. Few
people really use them, especially in this era of 99% plus automatic
transmissions. My personal experience is that these decorative items
are not sufficiently accurate for use. For instance, if your surface
skimmer is set up to run at 3600rpm, and you want to make a power
setting of 80% power, the rpm will change to 3344rpm a small difference
for some inaccurate tachs.
Most important use of the tach is when one unfamiliar with the craft
has pulled power well back to slow down for a turn, and wishes to know
where the power is during that turn, as reflected from past experiences
with the craft and the same power setting. I have gone without a tach
on some smaller craft, however, and driven just by feel. A tach is
vital for research and design, for instance, for performance comparison
of individual rotor and drive configurations.
Barry Palmer, for Sevtec
There have been digital tachs with decorative faces that worked well,
and I once purchased 4 of them, one worked, the others, I got units
with incomplete innards that were just stuck in a box and shipped!
The tiny tach either does not work or works accurately. If it does not
work, fiddling with the pickup wire will usually make it work.
Barry Palmer, for Sevtec