Periodic Error Correction, or PEC, is used to improve tracking in advanced telescope mounts. PEMPro, which is stands for Periodic Error Management Professional, is the most advanced commercial application software package for creating PEC curves for consumer telescopes. It makes it very easy to characterize and reduce the periodic error of your telescope mount.

New and improved features in PEMPro V3

Numerous user interface changes to make PEMPro visually more current, easier to used, and more intuitive.

Support for new cameras and camera control programs including:

o All cameras with an ASCOM Camera driver

o Sequence Generator Pro

o PEMPro-enhanced PHD2 (free download)

oTheSkyX Camera Add On

Improved support for cameras and camera control programs previously supported in PEMPro V2:

oAll Cameras supported by MaximDL Pro v4, v5, and v6

oCCDSoft V5


oMeade DSI series

oAll video cameras that have standard Direct Show or WDM drivers.

An improved Create PEC curve window to better select wanted and filter unwanted frequencies.

A new 3D FFT graph shows frequency/time relationships.

Numerous user interface improvements have been made to the Polar Alignment Wizard.

The Backlash exerciser now supports the ASCOM MoveAxis method.

One-click PEC automated the whole process of programming periodic error for some mounts (coming soon).

Programmable API to automate PEMPro (coming soon).

Programmable API to allow mount vendors to add support for their own mounts (coming soon).

Polar alignment via Plate Solving (coming soon)



Frequency Spectrum - Allows you to analyze what fundamental frequencies are present in your mount.

Polar Alignment Wizard - Quickly, accurately, and easily helps you dial in polar alignment.

Backlash Exerciser - Checks the backlash of your mount.

Star Finder - Helpful if you have a small CCD field of view to locate a star or other object when your mount's alignment is not perfect.

Video Interface - Provides a low cost way to use PEMPro using a web cam. No extra software is required.

Meade DSI Support - Native support for the full line of Meade DSI cameras.

What is Periodic Error and why should I care about it?

All telescope drives, including professional drives, have mechanical imperfections in the gears and worm, and the worm wheel that ultimately points the telescope.  These imperfections occur with a period determined by the rotational speed of the driving worm gear, but there can also be significant effects from other gears in the RA gear train.  If not corrected it makes taking unguided images impossible with even moderate focal length telescopes. Even auto-guided imaging is made more difficult because of periodic error. It is much better if the periodic error is corrected before the auto-guider has to correct it. When PEC is applied autoguided imaging can be more accurate and produce tighter stars.

What is Periodic Error Correction?

Almost all telescope drives made for astrophotography have some sort of Periodic Error Correction (PEC) facility, even inexpensive mounts. The purpose of PEC is to compensate for the mechanical imperfections in the RA motion of the telescope caused by imperfections in the drive.  Note that some mounts have a different name for PEC such as PEM (Astro-Physics, Inc.) and SmartDrive (Meade).

Typical ways to train your mount's PEC feature

Manually with cross-hair eyepiece. This is very tedious but can produce good results.

With an Auto-guider - limited by seeing and the accuracy of software and hardware control. Also the time delay between autoguider image acquisition and mount movement reduces the accuracy of the corrections. Frequencies that cannot be corrected with PEC might get programmed into the mount.

With PEMPro periodic error is collected over multiple cycles and modeled before being written back to the mount. Effects of seeing and delays in image acquisition are eliminated. Frequencies that cannot be corrected with PEC can also be eliminated.

PEC Work flow

The process of using PEMPro is very simple, but you will need a telescope and CCD camera that optimally provides at least 1.5 arc-seconds/pixel resolution for the best results.

1.Acquire PE Data.

2.Load the PE data for analysis.

3.Create a fitted PE curve to the data.

4.Program the mount with the PE curve.

5.Verify PE has been corrected by acquiring PE data again

For more details check out this section

Software required/supported

Windows 7 32/64, Windows 8.x 32/64, Windows 10 32/64 bit.

Microsoft Windows .Net Framework v4.5.2:

ASCOM Platform 6.3 or later:

The latest ASCOM Telescope Driver installation.

For Software Bisque Paramount mounts: TheSky5/6/XDirectShow webcam drivers or

One of these cameras drivers or applications:

oASCOM Camera driver

oMeade Autostar Suite and DSI (I, II, and III) series camera. More Details Here!

oDirectShow drivers for a webcam or video camera

Or, if none of the cameras drivers above applies, then one of these third party Camera control applications:

oSequence Generator Pro v2.6.0.25 or later

oDiffraction Limited MaximDL/CCD v3.22, or v4.x, V5.0 Pro, V6.0 Pro or later:

oSoftware Bisque TheSkyX Pro with Camera Add On

oSoftware Bisque CCDSoft v5.00.170 or later.

oAstroArt V3 with Service Pack 3, AstroArt V4, AstroArt V5, or later.


Supported Cameras

Webcams and video cameras with Windows WDM or DirectShow drivers.

ASCOM Cameras

Meade DSI camera line

Sequence Generator Pro (all cameras supported by this application)

PHD2 (PEMPro Enhanced version - free download)

Diffraction Limited MaximDL/CCD v3.22, or v4.x, V5.0 Pro, V6.0 Pro or later:

TheSkyX Camera Add On (all cameras supported by this application)

CCDSoft V5  (all cameras supported by this application)

AstroArt V3 or later  (all cameras supported by this application)


Supported Mounts


PEMPro supports any mount that has a PEC record feature. Here is a partial list of supported mounts:


Please click this link for a list of mounts supported by PEMPro.


IMPORTANT: PEMPro can upload PEC data directly to some mounts. You should use the procedure below if your mount is one of these types:


Astro-Physics mounts with the GTOCP3 or GTOCP4 controller

Celestron CGE, CPC, and Nextstar Mounts

EQMOD controlled mounts including Orion Sirius EQ-G, Orion Atlas EQ-G, EQ6, EQ5, etc.

Gemini G-42 Pulsar Equipped Mounts

Mounts with Gemini Level 4

Meade LX-200GPS and LX-200R with Firmware 2.x or later

Meade RCX-400 and MaxMount

Meade Classic 16"

Software Bisque Paramount GT1100S, Paramount ME, Paraamount ME-II, and Parmount MX


Computer hardware required by PEMPro

Computer CPU equivalent to a 500 MHz Pentium III or faster

512 MB or more of RAM (1 GB or more is recommended)

200 MB or more of Disk space

Monitor with 960x600 or higher resolution and 64,000 colors, 1280x1024 or higher resolution and 24-bit color recommended.

One of the supported cameras listed above

One of the supported mounts or telescopes listed above

No autoguider is required, the main camera is used to acquire periodic error data.