Interpreting Royal Navy Reserve record (enrolled 1900)?

[bugbear]

I have found, for a previous brickwall ancestor, a Royal Navy Reserve record (downloaded free from the National Archive).

Lots (and lots...) of information on it.

Are there any detailed guides to interpreting these? The layout is dense and complex, and the abbreviations numerous and opaque.

A specific question: Are these things that look like fractions actually dates? Does this say "Roxburgh" (presumably HMS Roxburgh) 24 March 1910 until 20 April 1910, 28 days ?

[Jebber]

Simply answer Yes.

[HMac]

There are no real guides for interpreting them only the eyes of experience. The records are quite messy, difficult to read in most cases. If there is any part of it that you would like us to take a shot at please post it.
Regards
Hugh 

[bugbear]

This isn't an interpretation question. His service number is U 878 (which was useful to find a medal award in Ancestry). But the card also shows 10 years previous service under

P 4478
Q 2354

I cannot find the service records for these numbers. I've tried searching in Ancestry and the National Archive with no success.

Can anyone with a better knowledge of where the records are kept and how they're indexed help me?

[HMac]

A reservist will have a different service number for each 5 year term. Unfortunately some have not survived but there are other sample cards held in BT 164 at TNA Kew but appear to stop short of  your range of P and Q numbers. There is another sample in BT 164/20 but I see no link for him.
Regards
Hugh