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# 1 sec vs 10 sec theodolite

## 1 sec vs 10 sec theodolite

(OP)
What is the accuracy difference between a 1 second vs a 10 second theodolite. I'll be locating trees on a 1 acre tree farm.

### RE: 1 sec vs 10 sec theodolite

Depends on the distance involved.

1 second at 100 ft is about 0.006 inches

TTFN

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### RE: 1 sec vs 10 sec theodolite

(OP)
Is there a formula that I can use.1 second at 300 feet is about how many inches?Thanks.

### RE: 1 sec vs 10 sec theodolite

The accuracy is approximately the tangent of the angle times the distance.  Call the accuracy "delta", then

Delta=Distance x tan (angle)

For 300 ft, 1 second:

Delta=300 x tan (1 sec/3600)=0.0015 ft = 0.02 inches

### RE: 1 sec vs 10 sec theodolite

(OP)
Thanks for the help.Chip

### RE: 1 sec vs 10 sec theodolite

For measuring trees, there is no difference in accuracy. Think of it this way - 1 arc-sec = the width of a dime viewed from 1.25 MILES away. So even with 10 arc-sec, you're looking at something the width of 10 dimes, about 5 inches, from 1.25 MILES. So across an acre, you'd be down do the 1/2 dime range or less. And, as usual, your setups and instrument leveling will degrade your readings more than anything.

Oh, and don't forget to use an offset measurement to get the center of tree measurement.

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