Good catch TK! I missed the "Tackymeter..." It does make one wonder...
ermmm, chaps please read this.
 On watches
Showing 35 seconds elapsed, about 103 units by calculationA tachymeter is the name of the scale sometimes inscribed around the rim of an analog watch. It can be used to compute speed based on travel time or measure distance based on speed. The function performed by a tachymeter is independent of the unit of distance (e.g. statute miles, nautical miles, kilometres, metres etc.) as long as the same unit of length is used for all calculations. It can also be used to measure an industrial production process in units per hour. A tachymeter is simply a means of converting elapsed time in seconds per X to X per hour.
 Measuring speed
To use a tachymeter-equipped watch for measuring speed, start the chronograph at a starting marker of a known distance. At the next marker, the point on the scale adjacent to the second hand indicates the speed (in distance between markers per hour) of travel between the two.
A standard tachymeter will only determine speeds greater than 60 units per hour using this method; slower speeds can be measured by decreasing the unit of measurement. Rarely, a tachymeter function is implemented in a fully digital watch, with digital display. Some watch sellers will use the term tachymeter incorrectly for a non-calculating seconds bezel.
The speed of an object is defined by the equation
The tachymeter scale computes the function
The spacings between the marks on the tachymeter dial are therefore proportional to 1/t where t is the elapsed time, or -log(t), and hence the tachymeter scale is sometimes also described as logarithmic.
The scale is generally only accurate for elapsed times over approximately 7 seconds. Some watches, not common, have 'wraparound' or 'scroll' scales, which extend the readings to lower speeds, typically 45 mph.
Some tachymeter scales are on a rotating, indexed bezel. This allows two additional modes of use: The tachymeter bezel can be aligned with a free running second hand, and, more subtly, can be used to average speed over longer times/distances. Set the rotary bezel index opposite the position of the minute hand, note the mileage. Glance at the tachymeter scale 60 units later, and average speed will be indicated. A little mental math allows interim averages, easiest at 1/4 (15 unit) and other integer values.
 Measuring distance
"I am enclosing two tickets to the first night of my new play; bring a friend, if you have one
- George Bernard Shaw to Winston Churchill.
"Cannot possibly attend first night, will attend second ... if there is one
- Winston Churchill, in response.