The most common and most likely answer to this crossword clue is the 12 letter word SPREADSHEETS
I've seen this crossword clue in The Daily Telegraph
S
P
R
E
A
D
S
H
E
E
T
S
Buddy explains!
The straight part
We know that "We might reckon on these" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case we might reckon on these = spreadsheets.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SPREADSHEETS mean?
SPREADSHEETS noun- A sheet of paper, marked with a grid, in which financial data is recorded and totals calculated manually.
- A computer simulation of such a system of recording tabular data, with totals and other formulas calculated automatically.