Good morning!
Would it be possible for you to share an image of the print that inspired this question? I'm afraid I do not quite understand what the calculator keys you're asking about look like.
In the absence of any image of the print, please consider the following.
Here are a few constructions that might work (without seeing the print, I can't say for sure which is correct).
If "E" is contained in a calculator key shape:
1.263996[E]-10
[simbraille]#1.263996$k,e]^-"10[/simbraille]
If both "E" and the "superscript minus" are contained in calculator key shapes:
1.263996[E][-]10
[simbraille]#1.263996$k,e]$k^-"]10[/simbraille]
If both "E" and "(superscript minus)10" are contained in calculator key shapes:
1.263996[E][-10]
[simbraille]#1.263996$k,e]$k^-"10][/simbraille]
Regardless of which of the above you use, please remember that the actual shape(s) used for calculator keys should be specified on the Transcriber's Notes page. And please do not hesitate to let me know if you have further questions or concerns.
–Kyle
edited by kdejute on 8/11/2015