The gap with the springs inside – that is not a reliable way to ensure it is level (the aluminium plate below can bend separately from the warping by the heatbed, giving very inconsistent results).

They way I do it:

1. Get yourself a Feeler Gauge (on Amazon or your local car spare dealer). You want at least a leaf of the layer height you will be using (for example I level with a 0.15mm gap, so I need the 0.15mm leaf/blade). I have a full set so I can change it very easily when I want
   1. A feeler gauge is simple a few leaves of preset thicknesses, which you can place into a gap to determine the size of the gap. By having an adjustable gap, now you can adjust it to be a very specific size.
2. Now level your printer and print out 2 identical posts –  http://www.thingiverse.com/thing:1138928
   1. Follow their instructions to make sure they are as close to identical as possible.
   2. A good idea is to mark each so that you will know which side you use for which post (keeping thing here consistent will improve results).
   3. Guide for Bed Leveling: https://3dprinterwiki.info/wiki/wanhao-duplicator-i3/duplicator-i3-calibration/bed-leveling/
3. Now place these posts under the X-rods (as shown in the picture they have).
   1. Move the rod down onto the posts, and let both sides skip steps (the posts will keep the X-rods firmly in place, and after both skipped steps, they should be level in relation to the posts).
4. Using the menu, move the Z axis up a few mm so that you can remove the posts.
5. Now home the printer.
6. Depending on which software you use to slice, you either need the gap to be 0mm (Simplify 3D) or the first layer height (Cura and others). If you need a 0 gap – it is difficult to level (how do you know it it just touching and not pushing down).
   1. Since I use S3D, I now command the printer through the menu to raise the Z to my first layer height (0.15mm), make sure you don’t use the fast option since that is full 1mm increments.
7. Now level the printer:
   1. What I use for quite consistent results is to use the menu to move each axis to predefined places (use the order on the guide) to level that position:
      1. Front Left: X10, Y10
      2. Front Right: X190, Y10
      3. Back Left: X10, Y190
      4. Back Right: X190, Y190
   2. Go over the places a few times (since each change can affect the leveling of the others), until you find they remain correct.
8. Now your bed is leveled in relation to your X axis, which should still (since we never disabled the steppers) be level in relation to your posts (which are repeatable).

Now you can print and test the leveling (remember glass can warp, which may through the leveling out in some places). You can also make minor adjustments until you get good first layers.

After prints, before you switch off the printer, raise the Z and place the posts in underneath, let it skip steps and then you can shut the printer off (the posts will keep it level and the next time you start the printer, just raise it again before homing).

This is how I have been printing the past few weeks (bit more than a month), and only did the whole leveling process when I moved the printer.