TI-81 manual Dad gave me his '81, and doesn't have the manual. He said I should be able to download it, but you only have a read in browser version. I need a download able version, as I have no way to reasonably transfer the whole manual page by page to my computer.

https://c.searspartsdirect.com/mmh/lis_pdf/OWNM/L0810016.pdf

Turn the calculator on. Press and release the 2ND key. Press and hold the up-arrow key to darken the screen/increase the contrast.

Obviously, to go the other way you use the down-arrow key instead of the up-arrow.

TI calculators have an annoying habit of dimming the screen when the batteries are changed so that it appears as if the calculator isn't turning on at all. Turn the calculator on (or at least press the ON key). Press and release the 2ND key. Press and hold the Up-arrow key for a few seconds and see whether the screen becomes legible.

Hi,
Any connectivity software for the Yexas Instruments cakculators is downloadable from the TI Support web site. Among the various versions available, I have not seen any relating to the TI81. However, it is possible that the TI Connect software can be used. I do not vouch for that. I have no TI81 to test it on.
Here is the link for all available connectivity software . If none works for you, I suggest you visit the ticalc.org archives. You might be lucky.

Hope it works

Unfortunately, the TI-81 doesn't have this capability built-in.

Unfortunately the TI-81, unlike later models, does not have this capability built-in. You'll have to find and load a program to do this.

As far as I know, the TI-81 doesn't have a degree-minute-second entry mode the later TIs have. But to answer your question, you can always do it as:
 35 + 20 / 60
followed by ENTER if needed.

If you're in Radian mode instead of Degree mode, you'd have to follow up with MATH 6 to specify degrees instead of radians.

Look on page 1-5 of this guidebook to adjust contrast.
http://education.ti.com/downloads/guidebooks/graphing/81/81$bookeng.pdf

TI calculators have an annoying habit of dimming the screen when the batteries are changed so that it appears as if the calculator isn't turning on. Turn the calculator on (or at least press the ON key). Press and release the 2ND key. Press and hold the Up-arrow key for a few seconds and see whether the screen becomes legible.

click on the link below or copy and paste into your browser, manual should open up in PDF doc just save it for future reference

http://education.ti.com/downloads/guidebooks/graphing/83p/83m$book-eng.pdf