SMART PHONE HEAT INPUT AND GAS RATE APP that can be use to time the gas meter for heat input or gas rate calculations. Inut the information into the box and press calculate and out comes:
GAS RATE.................... in M3/HR
HEAT INPUT (gross)..... in kW for older appliances
HEAT INPUT (net)........ in kW for newer appliances

it doesnt get much simpler no longwinded calculations to remember Instruction for use are here..

Even better now alterations can be made to the CV so calculations can be made for LPG
also you don't need to time the metric meter for two minutes anymore, the longer the meter is timed for the more accurate the calculation will be.

Now with a torch (for phones with a flash) makes life easier for meters under stairs or in cupboards.