The NASA task load index (TLX) is a procedure for accessing subjective task workload. It is a time-honored procedure used in HCI for over 20 years.
You can learn more about the NASA-TLX
My web version is based on a Windows program that performs the NASA-TLX.
The main difference in my implementation is I include the scale description alongside each scale. The descriptions were taken
verbatim from the original paper and pencil documentation.