From a6bcb82341c8e245e0eff9bd77f55f2d9d1e71b7 Mon Sep 17 00:00:00 2001 From: John Poole Date: Mon, 13 Sep 2021 09:20:56 -0700 Subject: [PATCH] Update glossary.md Defining ppm and giving example of how it is relevent --- design/glossary.md | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/design/glossary.md b/design/glossary.md index aa46ac1..86d1d46 100644 --- a/design/glossary.md +++ b/design/glossary.md @@ -13,6 +13,14 @@ successfully, a following *open* may assign the same id to a new recording. The open id disambiguates this and should be used whenever referring to a recording that may be unflushed. +*ppm:* Part Per Million. Crystal Clock accuracy is defined in terms of ppm or +parts per million and it gives a convenient way of comparing accuracies +of different crystal specifications. "A typical crystal has an error of +100ppm (ish) this translates as 100/1e6 or (1e-4)...So the total error on a day +is 86400 x 1e-4= 8.64 seconds per day. In a month you would loose +30x8.64 = 259 seconds or 4.32 minutes per month." +Source: https://www.best-microcontroller-projects.com/ppm.html + *recording:* the video from a (typically 1-minute) portion of an RTSP session. RTSP sessions are divided into recordings as a detail of the storage schema. See [schema.md](schema.md) for details. This concept is exposed