To make sure your level itself is accurate, take note of where your level measures a centred platform by observing the level's bubble, then flip your level around and re-check. If your level measures the platform the same evenly, then your level is accurate. If your level, once flipped, measures centre on a new plane then place a line between both measures and this will be the best centred measured line (Johnson Levels, 2014).
The wider the bubble is between the marked centred position on the tube of the level, the better quality your level is. The smaller the bubble is in the level's tube, the harder it will be to confidently identify a level plane (Johnson Levels, 2014).
The accuracy of laser-line-levels are measured through an industry standard of +/- (x)mm from a of a distance of at least 30m away. A laser line level with good accuracy is said to measure +/- 3mm @ 30m. With the same methodology a spirit level would be equivalent to +/-15mm @ 30m (Laser Levels Online, 2014). However, each of the levels mentioned below have a specific purpose during fabrication of a P&O device.
Levels will ensure the devices you make will be accurate, strong, and more importantly, biomechanically effective when correcting a pathologic gait.
Types of Levels
The most common and recognizable level, very versatile, usually rectangular. These are used during bench alignments, leveling wood blocks (also with a square), and just about everything else. Indicates 180, 90, and 45 degree level planes on flat surfaces.
Bull's Eye Level
A small, round, bubble level with a convex lens on one side with 'bull's eye' circular markings. They are used to measure a level plane on a very small surface, where a typical torpedo level may be too large. These are handy when bench aligning your prosthesis, from the SACH foot, to the pylon, to the socket adaptor.
A level that identifies to what numeric degree an object is tilted in. Zero degrees equalling a horizontally level surface. These can be used on KAFO's to ensure the uprights are on a level plane, or to keep a modified angle systematic through fabrication.
Plumb Bob Level
A pointed, weighted, metal pear shaped instrument that will maintain a vertical, or 'plumb', line (as opposed to the horizontal levels above). These are best used when approximating important weight lines through a lower limb prosthesis (similar to laser levels....but cheaper).
One of the more state-of-the-art levels, more expensive ones are self leveling. These levels use a laser to illuminate a plumb (vertical) and/or horizontal lines. Usually used on large three-dimensional surfaces that need both hands to work on or very uneven surfaces where many other levels may not work.
Did You Know?
"Spirit", "Bubble", Levels do not use water in their bubble tubes, but alcohol like Ethanol. Ethanol won't freeze and break in temperatures where many of these levels are commonly used. Ethanol also has low viscosity and surface tension which allows the bubble to smoothly flow through the tube (Encyclopedia Britannica, 2014).