Incorrectly written scientific notation

[KatieWoe]

Test device
Hooper and Dell
Operating System
iOS 12 and Win 10
Browser
Safari and Chrome
Problem description
For phetsims/qa#514. This does seem to occur in the published sim. On the second screen, it is possible to get two numbers on the side graph that should be equal, but are written differently, causing confusion. Specifically, you can have the number 1.0x10^-7 written as 10.0x10^-8, which is equal, but not scientific notation. This incorrect notation does also occur elsewhere, this is just how I encountered it, and seemed easiest to see due to how long it stayed that way. As you continue to change pH it does go to the correct notation.
Steps to reproduce

1. Go to the second screen and select blood as a solution.
2. Use the water and drain faucets to dilute the solution until pH is 7.
3. Observe the Concentration graph on the left and dilute a bit further, until the H3O+ concentration reaches 10.0x10^-8
4. Dilute further until concentration is 1.0x10^-7

Visuals

[pixelzoom]

This seems like something that should be fixed, unless there's pedagogical reason for it (which I doubt). @arouinfar your opinion?

[pixelzoom]

Reproduced.

To inspect the actual concentration values, I added this console output to LogarithmicGraphNode.js:

valueH3OProperty.link( value => console.log( `|H3O| = ${value}` ) );
valueOHProperty.link( value => console.log( `|OH| = ${value}` ) );

For the scenario that @KatieWoe described, the values printed to the browser console are:

|H3O| = 9.952541657737637e-8
|OH| = 1.0047684645685927e-7

Values are broken into mantissa and exponents by ScientificNotationNode.toScientificNotation. Using the above values:

> phet.sceneryPhet.ScientificNotationNode.toScientificNotation( 9.952541657737637e-8 )
{mantissa: "10.0", exponent: "-8"}
> phet.sceneryPhet.ScientificNotationNode.toScientificNotation( 1.0047684645685927e-7 )
{mantissa: "1.0", exponent: "-7"}

So this is a problem in ScientificNotationNode.toScientificNotation, and changing the behavior will affect all sims that use ScientificNotationNode, which includes: blackbody-spectrum, coulombs-law, gravity-force-lab, gravity-force-lab-basics.

[pixelzoom]

Tracking the general issue in phetsims/scenery-phet#613.

[pixelzoom]

Fixed in phetsims/scenery-phet#613. Patched in 1.4 branches for ph-scale and ph-scale-basics. Ready to regression test in next RC.

[arouinfar]

@pixelzoom it definitely doesn't serve a pedagogical purpose, and it looks like a possible reoccurrence of #2.

[pixelzoom]

@arouinfar gets the Super Sleuth award for locating #2 !! That facilitated further digging, and I discovered that this bug was (re)introduced by @jessegreenberg in phetsims/scenery-phet@bfa1874 on 9/20/17. I will note this in phetsims/scenery-phet#613.

[pixelzoom]

This is irrelevant for ph-scale-basics.

To verify in ph-scale, follow the steps to reproduce in #173 (comment).

[brooklynlash]

On Chromebook, the pH scientific notation is fixed for the blood solution on master.

[pixelzoom]

Thanks @brooklynlash. Closing.