# Reach module base precjsion

How much precision should emlid. Reach module base have in order in order to get cm level precision and correct fix on rover?

There isnâ€™t a certain single-value level that can be numerically represented.

What problems are you facing? Can you send us some images of your unit in use, so we can see the environment in which you are operating?

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Sometimes it gets incorrect fix

How can I guess whether I have correct fix or not?

Hi Giorgi,

Accuracy and precision questions are often tricky, but we are here to get down to it

The rover unit always calculates the position centimeter-precise relative to the baseâ€™s one while fixed. The shift in roverâ€™s coordinates can appear if you place the base on the same point but with different coordinates, for example.

I think the first thing we need to pay attention to is how you place the base station. Do you use averaging in single or enter the coordinates manually?

I use avaraging in single

Do you re-average the position each time you place the base on the same point?

Absolute accuracy requires a known point for the base, or the extra step of PPPâ€™ing your base. Choosing the applicable datum comes into play.

Relative accuracy to the base never changes as long as you do not change the base coordinates for the base location.

So depending if you require relative or absolute accuracy to the planet your base setup will require more or less work.

For your rover to be repeatable whether it is absolute or relative, you must not change the coordinates for your base position.

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Everything clear. Thanks

But, if I place base on known point and import base coordinates manually, wonâ€™t I be able tu get cm level precision even near trees and buildings if I have fix solution on rover? Am I right?

Likely not with the single frequency Reach module.
Emlid says that the sky view should not be blocked above 30 degrees.

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OK thanks

Hi Giorgi,

@PotatoFarmer and @wizprod have already provided clear explanations, so I barely have something to add here.

So, just to sum up:

• If you place the base on a known point and import base coordinates manually, and the rover calculates a fixed solution, your coordinates will be centimeter-precise.
• Reach Module is a single-frequency receiver that requires a clear sky view to calculate the fix.
• To work near trees and buildings, youâ€™ll need a couple of multi-band receivers such as Reach M2 or Reach RS2.

Thank you for your help and attention

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