Field Log Sheet

Fill this in at the site, not afterwards: conditions, equipment and readings as taken. A blank field means "not recorded" — never zero. One sheet covers a sightline run, a solar-noon shadow measurement and a levelling or water-level run.

How to use this sheet. Print it (or use Print → Save as PDF), and print at 100% — do not use "fit to page" if you can help it, so the sketch box comes out at the size you drew in. Write the predictions before you take the readings: a prediction made afterwards is not a prediction. Attach a photograph only if the conditions are written down beside it; a picture with no conditions is not a record.

Lasers. Never point a laser at a person, animal, vehicle or aircraft, and never sweep one across the sky — the same rule that stands on Try it yourself. The sun. Read the sun from a shadow, never by looking at it.

1. Where and when

Site name

Nearest town / grid ref

Date

Start / end time

Latitude, longitude

How position was found

Observer (name or handle)

Second observer / witness present

Water state (slack / flowing, tide stage, lock or weir)

2. Equipment

Instrument

Maker / model

Serial number

Target / staff / plate

Instrument height above water/surface

How that height was measured

Calibration checked before use (bubble, collimation, both faces)

Camera / phone, autofocus locked?

Distance measured how (map, tape, receiver, laser rangefinder)

3. Conditions at the time of the reading

Weather

Cloud cover

Wind

Air temperature (°C)

Water temperature (°C)

Relative humidity (%)

Air pressure, if noted

Where thermometers sat

Time conditions were noted

Atmospheric notes: haze, mirage, shimmer, inversion seen, sunrise time, anything that lifts or hides the line

4. Predictions, written before the reading

Globe relations, R = 6,371 km, refraction coefficient 0.13 (as on Try it yourself): drop d²÷(2R) (0.0785 m per km²); lift 0.13×that; horizon 3.57×√h km from height h m; sun altitude arctan(rod÷shadow). A level-earth reading predicts no drop and no lift.

Distance (km)	Predicted geometric drop (m)	Predicted refraction lift (m)	Predicted residual drop (m)
2.0	0.31	0.04	0.27
4.5	1.59	0.21	1.38
10.0	7.85	1.02	6.83

5. Results

Run	Distance (km) and how measured	Measured value, with unit and what it is	Predicted drop (m)	Predicted refraction lift (m)	Difference from the level line, and direction
A
B
B again, cooler morning
C
Repeat of the best run

Write what the instrument showed, not what it should have shown. A run that came out against your expectation belongs on this sheet, logged the same way as any other.

6. What was actually seen

Sketch: the sightline in section — instrument height, target, where the waterline sat, and any point where the line was cut.

7. Declaration

I filled in this sheet at the site, on the date written above. The readings under "Results" are what the instrument showed at the time. Where I could not check something, I have left it blank or written "not recorded" rather than an estimate. Where a figure is an estimate, it is marked as one. Conditions that changed during the run are noted as changes.

Observer — signature and date

Witness — signature and date