This is to make measurements on the helium that we use.
What we have used: https://www.gas-uk.co.uk/helium-10-litre.html
Working out how much we need:
Using the chart from https://ukhas.org.uk/guides:balloon_data?s=helium we've calculated using a 1000 totex balloon that we need 2.23 cu. m for a 500g payload. This translates to 3 litres of liquid helium. We would buy the 10 litre bottle from Gas-Uk, which should be enough for three flights.