Amy's Birthday by ACM a.k.a. Annie May
"Doctor, I think it's my birthday," Amy said in a moment of downtime, one of about three moments of downtime she'd had since stepping aboard the Tardis. "See, I've been making a mark here every time I go to sleep, and it's been the right number of nights now, so..."
She held up a small notebook.
The Doctor paused and set down an unidentifiable tool with which he had been poking the same section of wiring for the last twenty minutes.
"Nope! Actually it was a week ago, but you're very close. I wondered how long it would take you to notice!" he promptly declared.
Amy and Rory, who had just appeared over the Doctor's shoulder, were incredulous.
"How do you know?"
"Temporal monitor calibration!" said the Doctor, swinging a monitor around to face them. "I input the date (your time) that you arrived on the Tardis and the length of an Earth year and here it is! We can all measure our lives in Amelia Standard Time!"
Rory quietly asked the Doctor why their lives should be measured according to *her* arrival date. The Doctor gave him a look to remind him who was in charge before crying out, "Ow!" at the light punch he received from Amy.
"And why didn't you tell me until now?" Amy muttered, grinning in spite of herself.
"Sorry, sorry! But I think I can make it up to you! Here!"
Seemingly out of nowhere the Doctor produced a small box. It was wrapped in a crinkly copper-colored material and topped with a spinning gear.
"Alien," thought Amy, rolling her eyes.
A bit cautiously she removed the wrapping, concerned whatever was inside might be alive. Nothing leapt out to bite her, however. Instead she pulled out a very normal looking silver hairclip adorned with a tiny blue gem.
"Thank you, Doctor," she remarked, surprised at his taste. She put it on.
"Yes, yes, it's very pretty, whatever. But it's better than that! It's a temperamental indication device! Blue for happy, yellow for anxious, red for angry, and so on."
"Like a mood ring," said Amy.
"Well, yes, sort of, but far more accurate. Mood rings only use body temperature, whereas this actually monitors your brain waves to get a complete picture of your mental state and functions as a handy indicator light! So if you're angry, we'll all be a lot safer..." Here the gem turned purple and was rapidly growing redder, so the Doctor ducked beneath the console and shouted, "It was Rory's idea!"
Rory held up his hands and stuttered, "Uh, no, uh..." and finally stated sheepishly, "Sorry, I didn't know it was your birthday-"
"Last week!" cried the Doctor unhelpfully.
"But," Rory continued, reaching into his backpack, "I've been saving this just in case."
He handed her an unwrapped, rectangular box. She carefully lifted the lid to reveal a delicate gold chain with a star-shaped pendant.
"Seemed to fit, since it's your first birthday in the Tardis...and I thought it kind of goes with your earrings, so..."
Amy embraced Rory very enthusiastically and kissed him on the cheek.
"Well, thank you, both of you. Now, where are we going to celebrate?"
The Doctor only gave a mischievous smile and pulled the lever, sending the Tardis hurtling towards...somewhere.