is the vintage Estes AltiTrak. The one I had back in the 1970s was made of wood that went by the name
Altiscope (see below). The AltiTrak one is a newer incarnation made of plastic and is held like
Both models work on the right triangle completion principle. You stand off a predetermined distance
from where you expect the rocket to be at apogee (its high point of flight), and then follow it up with
your instrument. At the highest point, you lock the angle indicator on the protractor. You can see the
concept in the picture to the left (click for a larger version).
The base of the right angle angle is the side adjacent to the
measured angle (θ), which makes the vertical line to the apogee the side opposite the measured angle.
Since the tangent of an angle is equal to the quotient of the side opposite divided by the side adjacent
(which you determined at the beginning), that leaves the altitude being:
Altitude = Base * tan (θ)
Now, when I was a teenager trying to use my Altiscope, I didn't know a tangent from a schmangent.
Fortunately, Estes provided a table of values. Yes, teachers had attempted to learn me about trigonometry,
but I wasn't having any of it. As they did with many other rocket-related
topics, Estes produced a very nice pamphlet entitled "Estes Industries Technical
Report TR−3, Altitude Tracking," Cat. No. 651−TR−3. NASA has a
Altitude Tracking plan for building a simpler type of (here it is on
Archive.org in case NASA disappears due to being too White for them these
The Altiscope images below came from an
eBay listing. I sure wish I had gotten
Estes Altiscope Kit (Cat. No. 651-A-1)
Here is a list of my other rocket models.
Posted March 20, 2023