Fix: #2608: describe changing epsilon when configuring BigNumber.

HISTORY.md

@@ -1,5 +1,11 @@
 # History
 
+# unpublished changes since 10.6.4
+
+- Fix: #2608 clarify the docs on the need to configure a smaller `epsilon`
+  when using BigNumbers.
+
+
 # 2022-06-28, version 10.6.4
 
 - Improve TypeScript definitions of the `factory` function, thanks @mattvague.

docs/datatypes/bignumbers.md

@@ -23,15 +23,24 @@ BigNumbers instead of [numbers](numbers.md) by default, configure math.js like:
 math.config({
   number: 'BigNumber',      // Default type of number:
                             // 'number' (default), 'BigNumber', or 'Fraction'
-  precision: 64             // Number of significant digits for BigNumbers
+  precision: 64,            // Number of significant digits for BigNumbers
+  epsilon: 1e-60
 })
 
 // use math
 math.evaluate('0.1 + 0.2')  // BigNumber, 0.3
 ```
 
 The default precision for BigNumber is 64 digits, and can be configured with
-the option `precision`.
+the option `precision`. 
+
+Note that we also change the configuration of `epsilon` 
+to be close to the precision limit of our BigNumbers. `epsilon` is used for 
+example in relational and rounding functions (`equal`, `larger`, `smaller`, 
+`round`, `floor`, etc) to determine when a value is nearly equal, 
+see [Equality](numbers.md#equality). If we would leave `epsilon` unchanged, 
+having the default value of `1e-12`, we could get inaccurate and misleading 
+results since we're now working with a higher precision.
 
 
 ## Support