how to send a nat value other than a whole number

Question

How can I send a nat value to a contract that represents a data type which is not a whole number?

For example, the xtzToToken entrypoint of the tzBTC contract allows a user to call the xtzToToken entrypoint and send an argument of nat minTokensBought. If I want to send a value that is between 1 and 0 for this argument, how would I do so>

Here is what I've tried (unsuccessfully) via the tezos=client:

tezos-client --dry-run transfer 10000 from alice to KT1TxqZ8QtKvLu3V3JH7Gx58n7Co8pgtpQU5 \
                --entrypoint xtzToToken \
                --arg '(Pair "tz1eYpX4e1nu7e3cvtF7UvKFqUvWDahte1ot" (Pair 1/2 "2021-09-01T09:57:00Z"))' \
                --burn-cap 999

and

tezos-client --dry-run transfer 10000 from alice to KT1TxqZ8QtKvLu3V3JH7Gx58n7Co8pgtpQU5 \
                --entrypoint xtzToToken \
                --arg '(Pair "tz1eYpX4e1nu7e3cvtF7UvKFqUvWDahte1ot" (Pair 0.5 "2021-09-01T09:57:00Z"))' \
                --burn-cap 999 

Answer 1

Its not possible to send lower than 1 mutez. nat is also required to be a whole number.

Tezos/XTZ has 6 decimal places. When a user sees "1 XTZ" in an app, that is represented as 1000000 on the blockchain (6 zeros for 6 decimal places). The blockchain and RPC deal in this smaller scale (called mutez) and its up to each application to scale it up to XTZ when displaying to a user.

It is the same for all tokens. tzBTC has 8 decimal places, so 1 tzBTC, is made up of 100000000 satoshi's.

When you are doing this:

(Pair 1 "2021-09-01T09:57:00Z")

you are not sending 1 XTZ, you are sending 1 mutez (1/1000000 of an XTZ). Sending 1 XTZ would look like this:

(Pair 1000000 "2021-09-01T09:57:00Z")