Barometer

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A barometer is a device that gauges atmospheric pressure. It is used in Egypt to measure the altitude at the holder's location. Knowing your altitude is crucial to properly mixing a Ritual Tattoo, and is also helpful in planning Aqueduct routes.

Source

Made in a Glory Hole.

This item becomes available once you have begun the Test of the Ritual Tattoo.

Cost

• 1 Glass Pipe
• 1 Lead
• 1 Water in Jugs
• 3 Barometric Spheres.

Notes

Barometers, like other crafted tools, have a quality associated with them. A higher quality barometer is more accurate.

Final quality of a Barometer can be determined by doing the following formulas: Average = FLOOR((A + B + C) / 3).
Final quality = Average - ABS(Average - A) - ABS(Average - B) - ABS(Average - C)
Where A, B and C are the quality of the Barometric Spheres

Use

When carried, a new menu option becomes available under Special > Measure Altitude. This immediately reports the altitude of your current location in Main, in feet and inches.

Typical altitudes are 0 (sea level) - 600 feet (top of a tall 'mountain')

Accuracy

Data for a quality 1940 barometer

As in previous tales, barometers appear to report an altitude that varies according to the in-game time of day and the quality of the barometer.

The reported reading is the true altitude, plus or minus an error that follows a sine wave over the course of the game day:

 t = (egypt minutes since midnight) / (24*60)
 reported altitude = true altitude + E * sin(2*pi*t)

E is the maximum error of the barometer, which depends in some (currently unknown) way on the barometer's quality. E is smaller for higher quality barometers.

All barometers are perfectly accurate at 12AM and 12PM gametime (sin(0) = sin(pi) = 0), and are most inaccurate at 6AM (too high by E inches) and 6PM (too low by E inches).

Determining E

You can find E for a given barometer by measuring the altitude of exactly the same spot at 6AM gametime, then again at 6PM gametime. Convert the readings to inches, then:

 E = ((reading at 6AM) - (reading at 6PM)) / 2

It's best to use a flat area with an obvious marker to stand at, so that you can be sure you're measuring at the same spot each time.

Make sure your test spot is at least 10 feet above sea level, you don't want either reading to be 0.

Quality vs E

Quality	6AM reading	6PM reading	E (inches)	Notes
1	?	?	60	from the T2 wiki
1940	41' 10" (502 inches)	33' 0" (396 inches)	53	T4 verified
3734	73' 0" (864 inches)	65' 1" (781 inches)	47.5	T4 verified
6517	72' 0" (864 inches)	66' 1" (793 inches)	35.5	T4 verified
8007	71' 3" (855 inches)	66' 10" (802 inches)	26.5	T4 verified

Required By

Automatic Charcoal Production, Charcoal Brazier, Test of the Ritual Tattoo

Produced By

Barometric Sphere, Glory Hole