The XYL2b works for an office supply wholesaler (think bigger than Office Depot). She is always getting inundated with pen samples, so I use whatever she happens to have available for me to procure and feels good. 
That being said, a trusty semi-sharp pencil always tags along.
We also have a pair of natural pencil holders, one at each side of our head. Our 
73,
Guru just kidding
Normally I use my smartphone with a home made app that with an OTG cable allows me to answer in cw, you can see it in this video: QSO with @G4OBK .
I also carry a pencil as a backup, not a pen.
Brits of a certain age may remember another option, Guru
https://www.google.com/imgres?imgurl=http%3A%2F%2Fwww.bbc.co.uk%2Fstaticarchive%2F691c0ce32d038795e96062d95329921d5e9205ee.jpg&imgrefurl=http%3A%2F%2Fwww.bbc.co.uk%2Fcomedy%2Fblackadder%2Fepisodes%2Ffour%2Ffour_goodbyee.shtml&tbnid=f9iDommiBnWSrM&vet=12ahUKEwjj7JaxnsjtAhUT_IUKHYU0A2kQMygBegQIARAw..i&docid=RtRjxrJ61pBA-M&w=396&h=222&q=baldrick%20with%202%20pencils%20in%20his%20nose&client=safari&ved=2ahUKEwjj7JaxnsjtAhUT_IUKHYU0A2kQMygBegQIARAw
in US the stowaway spacepen is ten dollars +/- from REI and others. Weighs about 12 grams. I drilled a hole in the cap and tether it. The cartridge for it costs about six dollars and will fit in many other pens. 800+ activations in all conditions, never failed.Simple/robust/small/light/high altitude/rain/snow/won’t break/no smudging. - Fred KT5X / WS0TA
I’m glad you mentioned that. I had no idea that was a consideration. OTOH they carried a wooden slide rule because the metal ones could be a problem for electronics.
K7TP
All the slide rules I know of that were on Apollo missions were Pickett rules. Those are metal.
This article has more than you want to know about slide rules on Apollo missions. They were personal equipment, not supplied by NASA, so several different models went into space.
Personally, I prefer Post slide rules (laminated bamboo) and paper logs with a gel pen (dry weather) or a Rite-in-the-Rain ballpoint (wet weather).
wunder
Thank you. I now know more than I did a minute ago.
73
Grover K7TP
