# Measuring rotational angles in the field

### Introduction

So you're in the museum, measuring up a flute, and you're busily measuring lengths, diameters, thicknesses etc.  But then you realise, hey, I need to determine what angle of rotation the keys are at relative to the line of finger holes.  How on earth am I going to do that in the field?

Relatively easily actually.  But we are going to have to go back to primary school....

### Revision

How many degrees in a full circle?  360º.

That's it?  That's all we need?

### Method

1. Cut a thin strip of paper, long enough to wrap right around the flute in the area the angle measurement needs to be made.

2. Wrap the strip of paper around the flute, overlapping where the reference point is.  That's probably in line with the finger holes.

If you want to be really accurate, run a pencil line along the flute first using rule and pencil.  You can stick some tape to the flute first if you want to avoid drawing on it.  Alternatively use a pencil eraser to rub it off later.

3. Put a mark on both overlapping points in line with the reference.

4. Without letting the paper slip, put a mark at the angle you want to determine.

5. Remove the paper strip and lay it flat on the desk.  You have three marks.

6. Measure between the outside marks.  That tells us the girth (circumference) of the flute.  Let's call it C.

7. Measure between the the angle mark and the nearer of the overlapping marks.  That gives us the offset, O.

8. Calculate the offset in angle terms, rather than distance terms:  Angle = O/C*360.

### Example.

Lets assume we're measuring the angle of the C key compared to the line of finger holes.  We follow the instructions above and find:

Distance between overlapping marks, C = 78.5mm

Offset of C-key angle, O = 13.1mm

Calculation: Angle of offset = 13.1/78.6 *360 = 60º

### Conclusion

Now that wasn't so hard was it?  A really useful technique using virtually no equipment.

Created 13 March 2016