Altimeter: add BMP180 fractional digits

Fractional digits are already 2, add test.

Author: dnlup

lib/altimeter.js

@@ -69,6 +69,14 @@ var Controllers = {
     },
     toMeters: {
       value: function(raw) {
+        // Datasheet available at https://cdn-shop.adafruit.com/datasheets/BST-BMP180-DS000-09.pdf
+        //
+        // From Table 3, page 12
+        // Mode                    RMS noise
+        // ultra low power         0.5m
+        // standard                0.4m
+        // high resolution         0.3m
+        // ultra high resolution   0.25m
         return Fn.toFixed(raw, 2);
       }
     }

test/altimeter.js

@@ -456,7 +456,7 @@ exports["Altimeter - BMP180"] = {
   },
 
   resolution: function(test) {
-    test.expect(4);
+    test.expect(6);
 
     var driver = IMU.Drivers.get(this.board, "BMP180");
     var dataSpy = this.sandbox.spy();
@@ -475,6 +475,9 @@ exports["Altimeter - BMP180"] = {
 
     test.equal(this.altimeter.meters, 10.12);
     test.equal(this.altimeter.feet, 33.2);
+    test.equal(digits.fractional(this.altimeter.meters), 2);
+    test.equal(digits.fractional(this.altimeter.feet), 1);
+
     test.done();
   },
 };