Petrog® point count stage, quick instructions

The PetrogLite system is a computer-controlled, 2-axis point count “stepping-stage”, made by Conwy Valley Systems, Ltd. It includes the stage and stage control software subset of their larger Petrog system. There are several things you can do with this stage, but its main purpose is to set up a grid of points on a rock thin section. Then, under computer control, it moves the stage to each grid point, where you tell the computer which mineral is under the crosshairs. You have 26 (or 52) keyboard letters, each of which can be assigned to a mineral. The software tally’s up the points and calculates a percentage of each, giving a mineral mode.

Here are the software installation instructionspoint counter installation guide, and software user manual. Go to Conwy Valley Systems, Ltd. for software updates.

Quick instructions, this page
Illustrated instructions here
Stage installation here

Step 0

Set up the microscope for the stepping-stage, particularly removing the longer objectives (4x and maybe 10x objectives are OK). Also, decide which computer keyboard letters are for which phases. You have 26 case-insensitve letters A to Z, plus the spacebar for skipped points. Alternatively, you can set an option to have 52 letters, a to z and A to Z, plus the spacebar for skipped points.

Step 1

  1. Menu: Slide/Configure.
  2. Set the slide size to 4.6 x 2.7 cm (standard petrographic thin section, other sizes available).
  3. Set the number of steps (grid points) to count. Alternatively, you can select the step size option button to be explicit in terms of increments or microns in the X and Y directions.
  4. Keep the AoL button set to rectangular (other shapes available, round for example).

Step 2

  1. Menu: Slide/Area of Interest.
  2. In the left window, look at the Stepping Stage Limits section.
  3. Press the Bottom Left (origin) button. The stage should move to the origin position, NEAR BUT PROBABLY NOT ON where you want the bottom left corner of the grid to be.
  4. Use the “joypad” (right window) buttons to move the stage to the point where you want the bottom-left corner of the grid to be.
  5. Press the “Set as bottom left” button.
  6. Press the Centre button (why can’t those Brits learn to spel?).
  7. Use the joypad arrows to move to the point you want for the upper right grid corner.
  8. Press the Set As Top-Right button.

Step 3

  1. Menu: Slide/Logging Options.
  2. Set the check box to beep when an invalid key is pressed.
  3. Files are normally comma-separated ASCII text, but you can set other delimieters.
  4. The space bar is the skip key, allowing you to skip regions past the edge of the slide, for example.
  5. You can pick one or more isolated channels. These channels count key-presses, but are not tallied with the rest of the mineral key-presses. You can combine them later in a spreadsheet any way you want. Isolated channels are for things like void space, or something else you want to keep track of (not skip) but don’t want to tally with the minerals.
  6. Click on “Use backspace as undo-last while logging.” This lets you undo a mistake.
  7. Keep the rest of the defaults.

Step 4

  1. Menu: File/New.
  2. Type in your new file name and pick the file folder. The default folder is “Point count data” on the desktop. Alternatively, instead of making a new file you can pick an old one if, for example, you want to finish an interrupted run.

Step 5

  1. Menu: Logging/New or Logging/Resume.
  2. If you have just opened a new file (Step 4, immediately above), this opens the logging window and you can begin your point count. If an old file is open instead, you can resume logging where you left off last time.
  3. Start pressing keys to start logging. If logging doesn’t start and the stage remains motionless, press the “Annotate” button, then close the annotate window. That should clear the software bug.

More tips

  1. The tally file seems to be saved after every key-press. If you close the program, crash the computer, or have a power failure, all you have to do is re-start the program, and go to Menu: Logging/Resume to resume where you left off. If the program has forgotten which file, go to File/Re-Open to load your old file, then Logging/Resume. The stage will go back to your next point where you left off, and you can finish. The bottom line is that the point counting you have done is not lost, seemingly no matter how you stop the program.
  2. The screws that align and hold the point counter to the microscope stage are very tiny. Work over a big table so if you drop one, they won’t roll onto the floor and vanish forever.