Most Frequent Questions and Answers

Want to learn more about American Precision Gauge, LLC and our line of Linear Digital Measuring Devices (LDMD)? Read below or call us at 714-485-2365

The LDMD 3.0 is Inspected, Verified and correlated to a precision laser Interferometer traceable to NIST standards. Which means each LDMD created is meticulously checked in a multitude of conditions to understand the  accuracy or error inherent to each device. A report is generated showing reference points checked along the linear path with actual reading so as to compare the accuracy of the device relative to the laser readings. In this way, the error of the device is known and calculations can be made in the field as to where and how much to compensate for this error.

A Sample Print out is found here.

The LDMD 3.0 x 48″ is a stock item and typically ships in 3 to 5 business days. Preparation includes final inspection, reporting, recording, packaging and processing.

The LDMD 3.0 x 105″ is typically 3 – 4 weeks ARO 


Each LDMD slide extrusion comes in 56″ creating a 48.8″ measurable travel. As such, sections can be joined and pinned together to create virtually any length required. The one caveat to this creation is the unit must be fully supported and cannot be a stand alone gauge as with the 48″  travel LDMD 3.0.

We have developed a support structure using a typical aluminum profile extrusion with 40 mm x 80 mm profile with milled surfaces in the horizontal plane.

The LDMD 3.0 slide extrusion and the drilled and countersunk mounting holes is designed to match the extrusion channels and is held in place using 8mm button head fasteners and specialty t-nuts which AP Gauge can supply.

Most definetly.

The LDMD has a quick zero reset so blade touch off or part touch off is simple and accurate. Adaptive tooling or end of arm tooling can be easily attached for custom use. The limitation is IP rating. As long as digital display is protected and away from liquids. See IP Rating above.

The LDMD takes 2 AAA batteries and last 3 years with normal operation. Batteries are easily replaced with no loss of data and no reference reset required. Simply remove carriage, open battery compartment and replace batteries. Replace carriage and operate as normal. See Specification page and battery operations for more details.

Yes, the LDMD 3.0 can be used for measuring both OD as well as ID and Length.

Outside Dimensions can be measured with no programming needed. Close the jaws of the caliper so that the end plate and carriage paddle are in solid contact and then press the * (star button, aka; Store button) button on the display to zero the unit. Then open jaws, place work piece in between and close down touching the work piece to be measured and read the digital readout for dimensional information. 

Inside Dimension reading (ID) will require a simple programming change. Again, close the jaws by sliding the carriage paddle to solidly contact the end plate and zero the unit by pressing the * (star) key. Now, press the “P” (Programming) button on the digital display until “oFS” (Offset) is reached. Now enter an offset value equal to the thickness of the paddle and end plate combined (1.25″ typical). Once entered, press the * (star, aka:Store) button to store. 

Your LDMD is now ready to measure Inside Dimensions. Please refer to these links for further details: Operating Instructions and User Data

IP ratingfor the read head sensor is IP 67. The IP Rating for the magnetic tape and shielding is IP 54. The IP rating for the digital display is IP 40.

Thus, the greatest limitation is the digital display. Every effort must be made to keep the digital display clear of any misting, moisture, condensation, over spray or contaminants.

Otherwise the actuator portion and readhead sensors are well rated.

In the case of a cutoff application, typically the digital display is far enough away for the coolant flow as t not be an issue. Shorter cuts must be done in such a way as to protect the display.

Besides the IP 40 rating of the Digital Display, the next major concern for successful operation and long life of the LDMD 3.0 is magnetism. 

The encoding device is a Quasi-Incrementally Coded Magnetic Encoding Scale which uses magnetic poles spaced in such a way as to create a known separation. This spacing  is counted and recorded providing positional information to the display. Any distortion or interference of this magnetic scale could cause permanent and fatal damage to the  LDMD 3.0. Every effort must be made to keep any and all magnetic contact from the scale itself.  Protect this tape scale as you would your credit card magnetic coding.

If the magnetic scale is blemished or destroyed by magnetic contact, all is not lost. The tape can be removed and replaced. It is typically a factory replacement, but field replacements are possible. If this happens, contact AP Gauge immediately at 714-485-2365 or via

Yes. All components are capable of being replaced and are simple field fixes and can be done at the user level. This includes actuator components as well as read heads, digital displays and magnetic tape.

Any replacement of Tape, Read head sensor would require a re-calibration to insure continued accuracy.

AP Gauge does accept returns for repair and calibration at a nominal cost. 

Contact AP Gauge at 714-485-2365 or for details.

As shipped, the LDMD 3 weighs 12 pounds and the 105″ unit weighs 25 lbs. before mounting.

For best accuracy the LDMD 3.0 should be mounted to a solid, flat and fixed location with the work piece presented to the LDMD for inspection. However, the unit can be carried and used as a hand held device and as long as base is not bent, distorted or twisted the accuracy will be maintained. Obviously temperature, humidity environment play a roll in overall accuracy so environment must be considered in all cases.


The standard LDMD 3.0 comes with a battery operated LCD display with programmability and functionality. The limitation to this technology is the display accuracy. The standard LDMD 3.0 comes with an accuracy of within  .005″ of the nominal over the full travel.

AP Gauge has begun developing a more advanced and accurate display called the MA 100 display. This is a 110 V LCD display with limited programmability but excellent accuracy at +/- .002″ at 48″. Of course accuracy comes at a cost and the read head, tape scale and display increase cost of the standard by a factor of 2.

This increase in accuracy would require significant Engineering involvement and an email to would be required to begin the conversation.

Our Warranty and return policy is well documented and complete and is found here. For purposes here, the basic warranty and return policy is 1 year parts and labor assuming no mis-use or abuse has occured.

Normal hours of operation are:

Monday – Friday 9 am to 4 pm Pacific Standard Time (PST)

Payment is typical cash, company check, EFT or wire transfer. For wire transfer information please contact sales at 714-485-2365 or for further details.

Credit cards are not accepted.

Our phone is 1-714-485-2365 and our engineers are more than happy to assist. Also, or can offer whatever assistance you require.