Field tools

Run the math before you walk it.

These calculators match the operations on the disks. Use them to check yourself while you learn. In the field, do it on the instrument. Solar-time correction and sun azimuth cards print as letter, A4, 4×6, or 3×5.

Pace count

Set 100 m pace on D. C is distance, D is paces.

Distance walked
— m
Paces needed
— paces

Time · distance · speed

Same operation as C over D. Track the decimal yourself in the field.

Distance = S × T
—
Speed = D ÷ T
—
Time = D ÷ S
— h

Deliberate offset

Turn angle is never a clean 90°. Close distance = leg × sin(offset). LARS: offset right → turn left.

Travel azimuth
— °
Turn angle
— °
Close distance
— m
New azimuth after turn
— °

Slope factor

Ground = map × √(1 + grade²). 100% grade is 45° and 1.414×.

Slope angle
— °
Factor
— ×
Ground distance
— m

Noon-sun latitude

Latitude = 90 − (LAN altitude + declination). If declination is south, enter it negative. Northern hemisphere example: 45° altitude, +10° dec → 35° N.

Latitude
— °

Moon illumination

7% per day from full moon. Roughly ±10–15%. Good enough to decide whether to move.

Phase
—
Estimated illumination
— %

Sun compass season

Simple shadow methods are accurate when noon solar altitude is below 45°. Bagnold with a known sun azimuth is not bound to this table.

Northern usable window (approx.)
—
Approx. days
—

Solar-time correction

Flat disk, vertical gnomon. The 15°/hour clock is not latitude-correct. This sheet is minutes to add, by clock reading and month — then Equation of Time, longitude, and DST. Print or save as PDF.

  1. Level the disk. Gnomon vertical. 12 on the noon line, true south.
  2. Read the center of the gnomon shadow on the clock.
  3. Add the cell for this month. That is local apparent solar time.
  4. Mean = apparent − EOT (plot under the inner disk, or the EOT′ row).
  5. Longitude: 4 min per degree from the zone meridian. DST if in season.

In the print dialog choose “Save as PDF”. * marks a short shadow or a poor invert.

Sun azimuth cards

Bagnold-style tables for a sun compass: azimuth on the 1st of each month, and how many degrees it moves per day. Local solar time — not a watch until you apply Equation of Time and longitude. Print or save as PDF.

In the print dialog choose “Save as PDF”. Two pages: azimuth then daily change.

Educational approximations only. The disk’s engraved scales are the authority in the field. Cross-check anything that matters.