Impulse giggles.

Flash checks the monitors.

Warp's speed is still climbing. Mach 5.1, 5.2, 5.3...

"Want to see how this stuff works, while we're waiting for your brother?" he asks, but before Impulse can answer, someone clears their throat in the doorway.

"Flash. Care to explain the two latest additions to the clearance list?"

He looks at Impulse.

"I take it this is one of them?"

"Hi," he says cheerfully. "Impulse. Nice to meet you."

"Ah, Impulse independently recreated the superspeed formula," Flash explains.

"My scans picked them up making a trail of sonic booms across Canada. I offered them a position as my sidekicks, they accepted, and now we're doing powers testing. Warp is down there on the track, trying to find his top speed." 

He peers at the screen again. Are the numbers still climbing?

Yep. Pretty steadily.

"I see. And they come as a matched set?"

    "Seems like it, yeah."

Batman looks at Impulse, taking in his current expression, and back to Flash.

"Good luck," he says, in a tone that means you're going to need it.

Impulse giggles.

"Your League affiliate cards will be delivered in the next few days," he tells Impulse. 

"And - if Flash is willing to vouch for your suitability - you'll be eligible for full membership once you're eighteen, which would be...?"

"Next April."

"Hm." Batman, probably wisely, does not make any comments about Impulse's deceptively small stature.

"I'll leave you to it," he says instead, and turns to leave. 

"Bye!"

He turns back to the Flash.

"Yes, I absolutely do want to see how this stuff works."

"Somehow I thought you might."

He gives Impulse an overview of the system, not actually making any changes to the track yet. It's possible to add holographic obstacles varying from innocent bystanders to targets to enemies, all capable of moving. Some of them fire projectiles at the runner. 

"When Warp is done, I'll set you both running again and see how you deal with some of this." 

Gleeful bouncing seems to be his reaction so far!

"This place is so much fun."

"I'll be sure to pass on your compliments to the other designers," Flash says with a smile.

...he fiddles with some settings to temporarily disable the cameras monitoring the control room.

...Impulse looks up at him.

"Just because Batman probably already knows my secret identity," he says as he pushes back his mask, "doesn't mean I have to make it easy for him." 

Under the costume, Flash has short blond hair that he scrubs a hand through nervously.

"Hi. Barry Allen, pleased to meet you. I figure...you already showed me your face, and Batman all but said outright he's going to find out your name, so...it's only fair." 

...Of all the reactions Impulse could've had, a sudden fit of giggles probably wasn't the one Barry expected.

"Oh no we rhyme," he says, giggling. "Merry Nelson. Pleased to meet you too."

"I'd share my identity with your brother too, but - is he still going!?"

Flash - Barry - checks the readings again. 

7.0, 7.1, 7.2...

"Guess he hasn't found his top speed yet!"

"Acceleration's pretty steady...I don't think he's even close yet," Barry says almost to himself.

He switches views to an acceleration graph; once he factors in the need to slow down for corners, it's an almost perfectly straight line. Impulse's graph, in comparison, is much less smooth, although there's less data there. 

While he's at it, he pulls up a few of his own records, one from his first day using this facility and one from a week ago, to show Impulse the difference. The older one is wavering and inconsistent - this was back when Barry was still working on getting the hang of his superspeed. The newer one is a smooth curve, steeper than Warp can manage, but trailing off at the high end around Mach 10. 

"I wonder..." he says musingly, studying the graphs. "It looks like - you had the speed right from the start, you just couldn't figure out how to use it - and with Warp it seems more like he's - doing the same thing I did, just a lot more smoothly? I might be reading too much into it."

"No, you could be right," Barry muses. 

"Or it could be that Warp is more cautious than I was about increasing his speed, or has a natural talent for this, or both. Four speedsters isn't enough to identify any patterns for certain, especially when there's so little data from my predecessor."

"He's generally more cautious than me but that's not a high bar to clear..."